Large valved 273

too big does not work for lots of reasons
too big for the ports for one thing
and no reason for big exhaust at all
I'd start with the late 318 heads if stock heads
but then I'd use 30 degree seats with smaller cams in the 500 inch lift range
you can notch by hand- no need to notch the exhaust
flow does not like to hit top of cylinder, a little break can make a lot of difference
just reminiscing I think we took a 2.02 chevy valve and reduced the diameter to get a decent margin for a 30 degree seat and back cut them would have come out in the 1.94 area (you can't just re seat a 1.94 valve as they get too thin- 2.02 valves are cheap in any case- and lighter than MOPAR valves
measure twice cut once