Do you have the Edelbrock performer RPM cam, with those specs, or another brand? When you start adding "performance" parts, you need to have the adjustable valve train! Hardened pushrods, guide plates, custom pushrods and everything.
If you put it back together with out that stuff, you can look forward to another cam swap, really soon...
I have that same cam in my 68/289 Cougar. Nice cam, makes good power, (Needs more than a 3.50 gear, IMO)
I am on my second set of rocker arms and valve springs, and pushrods....In my case, it was getting sh!t info from my machine shop guy, AND my summit parts rep. They sold me chevy valve springs, and I was getting coil bind, with my stock Ford length push rods. ( there are 3 different lengths, FYI) Do it right, or do it again, your choice....(edit for spelling)