Update:

well, I finally made it out to the garage to do some measuring, etc. and take some pics. pics will get up here in the next few days.

the GM springs do fit as a drop on. on my particular set of heads, they are quite snug around the "pilot" area. that's the good news.

here's the (arguably) not so good news. the closest I could measure my installed height on my stock, looks to be original valve job heads, was 1.625" (1 5/8"). the 3.1L retainers actually reduced installed height by around 1/32" (to ~1.593" IH) using the mag keepers. using the 3.1L keepers, it increased IH to about 1.65", BUT, the tip of the valve was below the retainer, and the rockers hit the retainer first. if you've got a cam that's ~.45" lift or less with 1.5's, you should be ok with these springs as is.


for my project, using these springs, since I have a .462/.470 cam (will be .493/.501 with the mag rockers) I want to see my installed height to be at least 1.63", since these springs coil bind at about 1.065". that means

1) either the spring pad would need to be machined down ~1/32-1/16" to get adequate installed height, or
2) the valve will need to be sunk in about that amount with the valve job.

a bit of a bummer, but since the heads need a valve job anyway, it shouldn't be any added expense to sink the valves in 1/16", not like machining the spring pockets, which would be an additional operation, and an additional charge.

I wonder what effect sinking the valve into the head has for flow...


again, YMMV, et al.