The upward run (vertical narrowing) on the M76 receiver in front vs the stamped basically same plane of the PSL creates some little adjustments but mostly cosmetic.
Mag fitments and/or mods for feed are or can be big issues.., as you know. I recall you used the MG13 mag. I tried the MG13 and the M76 mag and they did not like the rimmed 54r cartridge. Would feed one side or flip up etc., on that cartridge rim. That was my initial setback until I decided to take the leap and open up the inside of the receiver for a PSL mag.
I got a modified Vepr single stack mag to feed reliably in the unmodified receiver but that was a step backwards really.
There is a fellow who profiled a barrel blank to M76 config in 54r. I might build a M76 complete build in 54r and use PSL mags now that I am fairly certain they will feed reliably and the receiver mod is doable.
Zastava made the M76 in 54r. I wish I had a few of their mags to use as it would make life easier.