Yet another 273 build advice thread!

remember you are comparing MOPAR at roughly .008 with the stock cam
with an aftermarket cam @.006
so the 260 comp is not a lot longer duration than the 252 as far as seat to seat duration -building cylinder pressure- Dynamic compression
more of the difference comes in the closer LCA with the aftermarket cam which build low end but narrows the torque curve
compare the ICL's and figure the intake closed point for both
If you look at the Melling and Elgin catalogs you can get more info on the stock cams
more of the difference is in the "intensity" where the aftermarket cam has it all over the stock cam (which will be more computer and emissions friendly)
X2 you can't do much to it without going easily overboard. (on duration) under 9:1

66 we sold a lot of E4s mostly for Y block Fords, interesting to see the difference with a Racer Brown