Gt 40 iron head trick flow springs longer then stock?

Very carefully verify exactly what you have. I did the spring upgrade to GT40 production heads from a Lightning truck. The valves have different heights at the retainer grooves due to the stock exhaust valves having rotators. The Comp Cams kit had two different retainers, iirc, one was .050 higher than the other. This allowed the springs ( I think all the same) to fit both intake and exhaust. Worked perfectly with bolt down rockers. The free length of the springs is not a good comparision, its the installed height, open and closed loads and max lift capability you are trying to get.