I rebuilt my 1967 3.4L engine last year.
The Churchill tool I borrowed from JCNA had a sizing diameter of 3.119". The crankshaft seal diameter was 3.125". So assuming no seal springback (unlikely) the crankshaft will compress the seal by at least 0.003" radially.
I did not trim the seal and the gasket set I used came from SNG Barratt as Payen EE532.
It was pretty hard to turn the crank after the seal was buttoned up. With the seal oiled, it took 25 lb.ft. to unstick the rotation, obviously less once it was turning.
The car has done 2000+ miles since the rebuild and there have been no obvious signs of oil leakage or other distress.
If you live in the US, I do recommend borrowing the Churchill tool from JCNA as all you pay is shipment in both directions as well as a security deposit.
This all may not be the cheapest way to go, but OTOH do you want to repeat the exercise if there’s a problem? I think doing it the way the maker intended is probably a good way.