The spring measurements were a mess. My equipment is not good, and work space is tight.
The 1.6" IH , measured with the 3100 retainers, that would yield a seat pressure of 124lb, and a .5" lift pressure of 306lb. The completed seat pressure is less cause the inst ht is 1.8 , these numbers are +/- bad testing equip. Got me a ball park and went with it. Have no cash, sometimes you have to experiment.
GM part numbers for these components are 10166343 for the valvesprings, and 10166344 for the retainers.
Summit headers 89 , and the fit is great. Nothing hangs down.