Well, I'm back with some good news. I've decided to go 124 front with EM rear, and I was able to get the rear element dialed in the way that I want it and ascertain sharp center and off center focus and have it match with the viewing lens. I have not been able to determine if I have serious light fall off at f/3.5. I did a quick comparison with my 124g and ground glass, and it seems almost the same, but I only spent a minute at most checking. I've been (unexpectedly) rather busy and I was roped into taking care of a friends' dog that is amazingly needy and mischievous at the same time. Combine that with my dog and it's total chaos.

At the rate this is going, I might not have to shim the lens board to compensate. I have done this before, if you're willing to search you'll find my first thread regarding my Yashicamats asking about shims (I called them washers, but same thing). And with regards to the wrecked 124 rear element -it's not that wrecked, before I bought the camera someone must have (inadvertently) stripped part of the coating on the outer edge, (probably) combating the same fungus. All I did was make it worse. It was either try it or find another exact donor camera, or spare front and rear groups. No biggie, really, like I said before it could be an interesting softening gimmick for a future project.

I wanted to use the EM front, but as the saying goes - "Spec. changes all the time, without warning". I'm not perfectly knowledgeable about EM's (mine was made in 1964), but either
A. The front name plate ring stripped from the rest of the lens housing (the part that says "Yashinon f/3.5 [some serial number]"), freeing the first glass piece from the surly bondage of professional abuse.
B. The front group was assembled piece by piece into a shutter, never meant to be disassembled, Which leaves me wondering how the other two elements in their housing got screwed into the shutter in the first place.

I'm sticking with A. It's kind of a shame, but the EM camera was destined for the dumpster (it was literally a "take my wife, please" kind of deal, it was that hopeless, and I used that camera as a learning experience. When I bought all three of them, none of them were functional, and I put a lot of effort into the 124's to get them functional. None of my work is contingent on them functioning, and I'm not trying to sucker someone by flipping. I do plan on keeping them. Also, I would never DIY repair a Rolleiflex or Hasselblad, only Yashicas and lesser cameras. So let's not get too upset over this.).

I have a roll of HP5 for it, I'll clue you all in a month from now in the future if it is successful (I'm backlogged). I do recognize that I am going where no man has gone before (and lived to tell the internet), that's why I made this thread.

/I wish I hadn't noticed my to/two mistake in my title. ugh!