It does sound like a heavy load for a standard diameter .904" flat tappet, but is 450 lb open really a "steep pressure" for the cam core itself? shruggy

My Mini-Express mushroom has about 430 lb open and doesn't moan or is stiff to turn. I'm pretty sure it uses the same diameter core but I could be wrong. Anyway I agree that whatever is making the cam hard to turn has to be corrected before you run it!