I understand Goldtone is revamping their banjos which is very needed, they traditionally do not have mastertone size resonators, new ones hopefully do.

Maybe they will since Greg Rich is working with them now.

This is what my good friend, AI says:

Yes, the resonator from a Gold Tone OB-3 will likely fit the Recording King RK-80. Both banjos are built to standard pre-war Gibson Mastertone specifications, meaning they share the same diameter (usually 14 inches) and use a standard one-piece flange.

Why They Should Fit:

Mastertone Dimensions: Both the Gold Tone OB-3 and Recording King RK-80 are 14-inch resonators with Mastertone-style flanges.
Lugs/Brackets: Both instruments utilize standard 24-bracket hardware, which means the sidewall cutouts on the OB-3 resonator are designed to clear the standard flange brackets on the RK-80.A

Few Things to Keep in Mind:
The "Drop-In" Factor: While the dimensions and specs align, minor variations can occur depending on the specific manufacturing runs or how your coordinator rods are adjusted. It will generally be a clean fit, but you may occasionally need to slightly loosen and retighten the brackets for perfectly flush seating.
Resonator Lugs: You will need the four resonator thumb screws / attachment hardware.

Thanks everybody, that’s what I was hoping to hear. I had an OB-250 a while back from when they were still manufacturing in Korea, so it had that odd size resonator.
I had heard they were moving to Mastertone spec sizes.

Because Gold Tone still describes its "Mastertone" resonators as "14 inch," I wrote to them not long ago to ask if that was exact or rounded up. They wrote back it's rounded. 

I suppose you've seen that Gold Tone is having a sale right now with "B stock" seconds or blemished items at good discount. 

Here's a B-stock OB-3 resonator for $225 ($75 off). The color might not be the same as an RK-80. But it will probably look good. No idea what the blemish is.

Be careful drilling holes for the wall lugs!

Many a banjo walks around shamefully wearing a hole in the resonator sidewall. Many a banjo is crippled with thumbscrews that won’t go all the way in, don’t line up, too. And they cannot run and play with the other banjos.

quote:

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Originally posted by Brett

Many a banjo walks around shamefully wearing a hole in the resonator sidewall. Many a banjo is crippled with thumbscrews that won’t go all the way in, don’t line up, too. And they cannot run and play with the other banjos.

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The old idiom "measure twice, cut once" is elevated to "measure thrice, drill once" when the stakes are high, and there is no room for a patch-up job. This approach relies on careful preparation and zero-error execution. 

I would wrapping a piece of masking tape around the drill bit to mark the stop depth. (Mr. Obvious)

Thanks for tag, if it helps, you can get by with two staggered resonator attachments, ala Kay and Vega, and could use three ala older Gibson. Either is easier to line up and keep straight etc.
Sources do dry up, BUT, there could be someone out there in radioland at this very moment with a badly broken neck, or twisted neck that they are willing to part out in response to a “I will pay top dollar for stock RK-80 resonator” advertisement.

Steve Davis on here mentioned pin vise, or pin drill, I looked on Amazon. Thats the best $20 a banjo guy could ever spend. It’s little drill you spin with fingers. Comes with several small bits to work your way up. The thing to have for spiking fingerboards. And wall lugs and so forth. The tabs you mount under the flange don’t look prewar, and may sit your pot deeper into reso but ease up lining stuff up too.

quote:

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Originally posted by ban-joe

I have an early RK-80 minus resonator that I’ve always wanted to make complete. Some of the builders here sometimes had an RK resonator for sale, but that source dried up eventually.
I now see GoldTone is selling “OB-3” finished resonators. They look identical to the old RK-80 resonators. I would buy one if I knew they would fit the RK-80 pot.
Anyone familiar with this product?

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Joe, 

Sent you a PM

Mike