Room for a Clutch-Fan in a '65?

When I first got my 65 Barracuda, it of course still had the Commando 273, 4 speed with 3.23 gears. And the 3.09 low gear, of course. Sort of consistent with AJ's comments, I could stay with an SS396 through low gear, but they would immediately jump out a full car length when I speed-shifted into second.

I didn't have that problem after I swapped in a 340.

As for the head gaskets, I haven't tried to find any for a 273 in many decades, but Mancini has steel shim head gaskets for a Mopar small block, that are .028 thick with a 4.14 gasket bore. Or Cometic has a set (C5633-027) that is .027 thick with a 4.04 gasket bore. Either has a larger bore than you need, but switching to these and milling the heads .030-.060 would help the CR a lot.