You're right to be cautious about the position of the neck heel lag screws and where the neck fingerboard will end up relative to the plane of the head.

Pretty much all Gibson necks use the same spacing. And the rim height is made to end up with correct height for whatever tone ring is on it: simple tone hoop, arch top, ball bearing, flat head. Now if you intend to put an arch top or flat head tone RING on a 100 style pot, you have to be mighty careful -- for anything other than a tone hoop the rim will have to be cut down some for the neck to fit correctly.

You're kind of going at this backwards from most folks. Usually one gets a 100 style pot first, perhaps a tenor or plectrum, and then scrounges about to find a suitable neck. You may gasp at the cost of a new Prucha pot. Prucha generally makes pots to Gibson specs, but it's best to ask for exact dimensions (in inches) and compare to your 100 neck. The key is the distance from the upper lag screw to the top of your fretted fingerboard. And then the distance between the upper and lower lag screw. The Classifieds often have used assembled pots; keep an eye on them. But remember to get the dimensions! Or buy an orphaned Gibson tenor or plectrum banjo looking for a home -- rescue the pot and orphan the 4 string heck. Gibson tenor and plectrum 100s can often be had for low prices.

Also, your 100 neck is made to fit on a Gibson ONE PIECE flange pot. You won't want to get into trying to "adjust" a one piece flange neck heel to fit to a two piece flange pot.

Two coord rods aren't really necessary. But having an upper rod does no harm either.

You've got an interesting quest -- good luck.

Thanks for the advice, this is exactly what I am looking for.

I’m in Germany, which does two things - Prucha prices are somewhat lower here, and there are no tariffs or other duties involved, which helps. Being in Europe also makes used parts scarce. So Prucha it is, unless something else comes along. An old Japanese Kasuga might be the only other realistic option. Direct order from Prucha of a pot, resonator (both unfinished) and the various other bits (tailpiece, armrest, resonator mounting, co-rods, lag screws) will be about €1300 which is fine. I’m sure I could call them and ask about the lag bolt holes. They can probably put them wherever I need.

FWIW, back in 1962 Walt Pittman fit an RB-100 neck to a 1926 PB-1 shell with a Mastertone ring on it. Worked just fine.

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Originally posted by stevo58

Thanks for the advice, this is exactly what I am looking for.

I’m in Germany, which does two things - Prucha prices are somewhat lower here, and there are no tariffs or other duties involved, which helps. Being in Europe also makes used parts scarce. So Prucha it is, unless something else comes along. An old Japanese Kasuga might be the only other realistic option. Direct order from Prucha of a pot, resonator (both unfinished) and the various other bits (tailpiece, armrest, resonator mounting, co-rods, lag screws) will be about €1300 which is fine. I’m sure I could call them and ask about the lag bolt holes. They can probably put them wherever I need.

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Speaking of old parts, you could always try contacting Norbert Pietsch (Brenen) and/or Bernd Gassmann (Mannheim area). They both have been a great  help in restoring my RB-1.

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Originally posted by RB-1

Speaking of old parts, you could always try contacting Norbert Pietsch (Brenen) and/or Bernd Gassmann (Mannheim area). They both have been a great  help in restoring my RB-1.

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That's an idea. Karsten Schnoor in Hamburg is another possibility. 

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Originally posted by stevo58

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Originally posted by RB-1

Speaking of old parts, you could always try contacting Norbert Pietsch (Bremen) and/or Bernd Gassmann (Mannheim area). They both have been a great  help in restoring my RB-1.

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That's an idea. Karsten Schnoor in Hamburg is another possibility. 

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Though I hold Karsten in high esteem, especially for more historical instruments, in my opinion Norbert and Bernd are the Gibson and Gibson-like specialists.

It's possible that the height of the lag screw to the top of the fingerboard won't match the tone ring, but I think it will be close to fitting. The lower lag bolt may be more off, however.

See how they line up when you get the pot. What I would probably do if the holes are almost right is use a round file to open the hole slightly in the direction they need to be. If they're way off, I would remove the lag screws, drill the hole bigger and glue in a hardwood dowel. Then I would redrill the holes and reinstall the lag bolts.