Okay; first off, with a user name like "Tbeausoleil," you damn sure better be from Thibodeaux. 
As to the rest:
Another term for "parts bass" is "Frankenbass": an assemblage of parts taken from other instruments. So you really don't design it as such. You get a mental image of the bass you'd like to have and then assemble the components that would result in that bass (or as close as you can come).
Bodies: Danelectro (Dano) bodies show up fairly frequently in online auctions, in the different configurations. They are light but will require routing if anything other than Dano pickups are used. Also, Dano bodies are not truly hollow in the conventional sense of the term. they are chambered, and one consequence of this is that they have a bit of "punch" that true hollowbodies lack. Harmony (including Silvertone), along with Kay and Regal, is a Chicago product, and there was a lot of inbreeding done among Chicago instrument factories. They were jobbers. In addition to their own marques, they would supply components -- usually bodies -- to spec for other companies (Gibson and Gretsch also were in on this, but to a much lesser extent). Harmony bodies offer the Venetian (rounded) cutaway with dula f-holes and can be found in single and double cutaway versions routed for one, two, or three pickups. Kay bodies have a Florentine (pointed) cutaway and are routed for one, two, or three pickups and may be found with no, one, or two f-holes. These bodies all are fully hollow.
Necks: Necks also are ubiquitous on online auctions. First you have to decide whether you want a short-scale (30") or long-scale (34") bass and purchase a neck made to that appropriate scale. Hollow body basses in the main use trapeze tailpieces and floating bridges, so getting the bridge in the right place is not an issue. Suitable tailpieces and bridges also are not hard to find.
Don't worry too much at first about neck heel/pocket fit. A heel too small for its pocket can be widened with shims, and one too wide can be narrowed with a Dremel tool and scrapers. For ergonomic reasons you may want to give some thought to total length. A long-scale hollow body bass can be beastly, wicked long.
Pickups: The original H22 had a pickup from Rowe-DeArmond, the leading jobbers for pickups in that era. These also are not hard to find online, and a pickup from a guitar should serve you just as well as one from a bass. Whatever you choose, just be sure the pickup will fit well into the pickup hole(s) in the body. You really don't want to have to do woodwork there.
Electronics: No comment from me. I can solder capably, but figuring out how the wires go is a skill I have not mastered yet. There are plenty of folks on TB who can help you with this. Just be aware that this is the part most likely to be an ordeal, as the entry and exit point for hollow body electronics will be either through the sound hole or through the pickup routes. Patience is a virtue.
As to the rest:Another term for "parts bass" is "Frankenbass": an assemblage of parts taken from other instruments. So you really don't design it as such. You get a mental image of the bass you'd like to have and then assemble the components that would result in that bass (or as close as you can come).
Bodies: Danelectro (Dano) bodies show up fairly frequently in online auctions, in the different configurations. They are light but will require routing if anything other than Dano pickups are used. Also, Dano bodies are not truly hollow in the conventional sense of the term. they are chambered, and one consequence of this is that they have a bit of "punch" that true hollowbodies lack. Harmony (including Silvertone), along with Kay and Regal, is a Chicago product, and there was a lot of inbreeding done among Chicago instrument factories. They were jobbers. In addition to their own marques, they would supply components -- usually bodies -- to spec for other companies (Gibson and Gretsch also were in on this, but to a much lesser extent). Harmony bodies offer the Venetian (rounded) cutaway with dula f-holes and can be found in single and double cutaway versions routed for one, two, or three pickups. Kay bodies have a Florentine (pointed) cutaway and are routed for one, two, or three pickups and may be found with no, one, or two f-holes. These bodies all are fully hollow.
Necks: Necks also are ubiquitous on online auctions. First you have to decide whether you want a short-scale (30") or long-scale (34") bass and purchase a neck made to that appropriate scale. Hollow body basses in the main use trapeze tailpieces and floating bridges, so getting the bridge in the right place is not an issue. Suitable tailpieces and bridges also are not hard to find.
Don't worry too much at first about neck heel/pocket fit. A heel too small for its pocket can be widened with shims, and one too wide can be narrowed with a Dremel tool and scrapers. For ergonomic reasons you may want to give some thought to total length. A long-scale hollow body bass can be beastly, wicked long.
Pickups: The original H22 had a pickup from Rowe-DeArmond, the leading jobbers for pickups in that era. These also are not hard to find online, and a pickup from a guitar should serve you just as well as one from a bass. Whatever you choose, just be sure the pickup will fit well into the pickup hole(s) in the body. You really don't want to have to do woodwork there.
Electronics: No comment from me. I can solder capably, but figuring out how the wires go is a skill I have not mastered yet. There are plenty of folks on TB who can help you with this. Just be aware that this is the part most likely to be an ordeal, as the entry and exit point for hollow body electronics will be either through the sound hole or through the pickup routes. Patience is a virtue.
