Building a budget TPI motor with LT4 hot cam and Vortec heads.
I know its common to use the LS6 spring but everyone says to use the Comp retainers. Is there any reason I can't use the LS6 retainers I already have them and free is a lot better than $75.00 if I can use them.

 

Because the LS retainers are the wrong ones to use, the LS engines have smaller valve stems and valve locks are also different.

Comp 787 is what you want for a standard SBC Vortec head with LS6 springs.

 

You could also consider LT4 springs, 10° locks, and titanium retainers. Under a Benji for the whole lot:
12495494 https://www.gmperformancemotor.com/parts/12495494.html
12495492 https://www.gmpartsgiant.com/parts/g...-12495492.html
12495503 https://www.gmperformancemotor.com/parts/12495503.html

 

LS valve stems are 8mm (about .3149"); SBC are 11/32" (.34375")

Gotta use retainers that have the LS spring outer dia but fit your stems. Which is, Comp 787. There may be others but that's the one I know of offhand. There are no stock ones with the right combo of dimensions, obviously.