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I am putting a new 408 in my car, yesterday I went to set the valves and realized that my roller rockers are hitting the side of the valve retaing cap and floating above my valve. I ordered a puchrod checker suppose to be here this week I was already using a +.2 .

So back to my question has anybody used lash caps before?

Yes I have but only if necessary for geometry or with Titanium valves without hard tips
By pushrod checker & hope you mean adjustable pushrods & not one of those cheesy plastic POS deals that are as useless as tits on a boar hog,,-
You can only use lash caps if you have the correct locks or you have a tall enough valve stems, the tips cannot touch the locks
What rocker & spring are you using that is causing a problem?

The heads are AFR SBC 210cc Competition, with 1.550" OD Roller Dual Valve Spring w/ dampener, 225 lbs on seat, .710" maximum lift,they locks are the correct lock for lash caps. the rockers are Comp cams ultra-gold aluminum 7/16 1.5

The puch rod checker is a comp ajustable puchrod

If I had to guess I would say your pushrod is too short but I have never used the Comp aluminum rocker so it is just a guess
I have used the heads a few times as I am a WD for AFR but they had shaft rockers on them with no issues except pushrod clearance
If it turns out to be a shitty rocker design problem you should be able to band-aid it with lash caps to move everything up as long as you have enough stud but it would not be my first choice as a fix
Clearancing the rocker would be what I would do, that or changing them to something else