It says the springs must be modified. The assault heads dual springs are good to go for that right? It also says the heads must be machined. The assault heads are good to .650" lift so theyll work as is correct?[/QUOTE] You will need to purchase valve springs that the cam manufacturer recommend for the camshaft. The springs that come installed on the heads are for hyd. flat tappet camshafts.
K12-444-8 XR300HR uses 987-16 valve springs, best roller rockers 19001-16, and push rods 7809-16.