I'm planning to replace the heads on a 1987 460 engine and I see that there are 3 exhaust manifold studs already sheared off. Any ideas on how I can prevent others from breaking when I try to remove them (other than WD-40 or PB)? The engine is in a motorhome with 31K miles. Given the low mileage, would it also make sense to change the hydraulic valve tappets while I have the heads off?
I don't have any special tricks for preventing corroded studs from breaking during disassembly; somebody else might. You will probably need to repair those threaded holes while the heads are off the engine.
I do not recommend changing out the hydraulic lifters as they are broken in with the camshaft. 31K miles is little time on them anyway.
for the heads- a good 5lb dead-blow hammer works pretty good for knocking them loose. the intake just use a flathead screwdriver and pry up the front- the front and rear seals suck anyways so when you throw the intake back down just use a bead of high temp rtv silicone on the front and back... just make sure you let it cure for a couple minutes before putting the intake back down.