Hmmm. I only had problems with the pushrods on my exhaust valves, because my cam has a reduced base circle on exhaust only. Lash caps fixed that. Intake valves no issues.
More'n likely need to change pushrods as the valves in your heads (if they're the stock length) are quite a bit shorter than the valves in the GT40 heads. As for the springs, you need to check the recommended specs of what your cam needs. There is a chance that the GT40 springs are stiff enough for a solid lifter flat tappet cam. They don't have to be "dead on" as far as the compressed and open rates, just close to it.
