Brent has a very good idea, I haven't tried it, but absolutely worth a shot. Heard a lot about a little dressing of the bottom of bearings on the outside, but never did it. Likely could work for the slightly tight ones too
I am not an FM hater, but I am drifting away. I like the main bearing design, but have gone full groove mains on the last 3 on the mains because I couldn't get the numbers I want, and I have pretty much given up on FM rod bearings and gone Clevite. I have seen the FM mains and rods loose, tapered, and not the same as each other.
I would measure your main bore and make sure there is no taper and if it's in the bearing, I'd probably consider a set from a different brand as an experiment, even if it was a cheapo set you could sacrifice if you decide to polish and fit if things are repeatable.
I hate to admit it, but on my own temporary F100 engine, a 390 bench build (as in all the parts laying around under the bench) build I used Enginetech...squirmed when I took them out of the box, a real odd bearing, aluminum shell, but all the numbers came in spot on and it didn't miss a beat
FWIW, I have 2 sets of FM rod bearings I keep trying to use, over a few builds now, they always come up loose, one set had a chunk of something embedded in it. Bought a set of narrowed Clevite, and it's like a production shop assembling the rods. Once I got a combo for one rod, every other one was the same.