the 6.1 is only 16 cubic inches or so bigger than the 5.7-------not an issue that should show any significant issues in a street driven rod--

On the older rebuildable engines----------the issues with todays fuels and oils on exhaust valve seats and tappets/camshafts---------not worth the drama of rebuilding old heads unless someone is doing a numbers matching restoration----and that cams/lifters need to be changed to rollers which can be expensive!!!!
In the sb chev-there are roller camed cores available which can be fitted with alum aftermarket heads and then you can do either the carb or efi route.
Mopars-late 360magnums from pickups would be usable and could also be retro to carbs for period under hood look
As for what I'd use--I'd use something that the current political correct auto supply houses and dealers carried parts for-------on the road cooling , fuel supply, etc issues will just get you a long $$$$$$$$$$$$ride in a tow truck

The modern Ford and Mopar over head cam motors take up a lot of space and are hard to work on------the GM LS motors are light and can be simple-------

ME??????? I'd put a hemi in it and think I got 3 of the late models out there somewhere plus the 392 sittin by my flathead ford---------But they are expensive to rebuild--------and I got a full machine shop