Just wanted to pass this along. We sent a head to zforce motorsports (zfore227) on ebay and the results were fantastic.
The original purpose was to just have the seats cut with an airfloat cutter to get a great seal on the new factory Yamaha valves for a 225DX head, to take full advantage up the bump in compression from the XT225 piston. Although he doesn't list every single air-cooled 2 valve head for service on ebay, I just sent him an email asking if I could just purchase the service for a CRF50 and send in the 225DX head instead. He said yes, no problem.
Head was cleaned decently, disassembled and sent with new valves, and all of the rest of the valvetrain parts. Came back, head was blasted, the deck had been machined flat, valve seats cut, exhaust port was cleaned up and everything was assembled. The engine fired up right away and after some jetting has surpassed my performance expectation. It legitimately feels like the power doubled from a piston (stock size but can be gotten at 1mm over, special order 2mm over), head work, intake and exhaust. The DG is way too loud, it sounds like a beast.
I think the head work made a huge difference and at 80 bucks total for shipping and service it was a great deal for something I don't have the tools to accomplish. I have no affilliation with the guy he just does good work and deserves the mention, and there's always been a lot of issues here with people that would have saved time and $ by sending their head to him, and ended up with more power.
He has 100% feedback which is how it should be for an engine builder. Not like some Disney characters I know of.
Here is the link to the CRF50 auction, be sure to email him and let him know what you'll be sending, but he told me any air cooled 2 valve head is fine:
https://www.ebay.com/itm/HONDA-CRF50...YAAMXQHDlRcL9r
Here is a pic of the bike finished, I will look for and post any build/engine build pics i have if anyone wants details. I think there is video of it running for the first time somewhere. It just wasn't a big deal to document the build this time, just wanted to get it built.