Hello Roger,
If you haven't so far, download a copy of the Y2K manual R3.......
http://www.r-390a.net/Y2K-R3/index.htmAnother great source of info; experts on the R-390/A......
http://mailman.qth.net/mailman/listinfo/r-390So what you are saying; the parts radio IF deck works in both receivers. The IF deck mentioned first has limiter issues. In the Y2K manual Chapter 5, figure 5-6 shows tube voltages & resistance. Check those first......tube extenders help!!
I can think of other items, but would have to know what else has been done to the receiver.
Regards,
Craig