273 time to 'fish or cut bait'...

901 springs. Are 87.5 lb @ 1.700 in closed and 227.75 lb @ 1.275 in open. A .06 spring shim will add 19.8 lb to each position. Plenty good for an E-4 Isky cam. You have closed chamber heads, I stand by my recommendation of 2 barrel pistons unless you are boring the block. 273 2 barrel pistons are only .020 in the hole. Now is the time to measure with the heads off. The springs are the only difference in Commando heads. I have new valves, let me know and I can cut you a deal. Use the good Viton valve seals while you are at it. There are sound bites of the E-4 cam, both mine and Mike's.