Advice needed

The XE275HL is a fairly mild hydraulic for a 408 stroker.

Remember strokers will soak up around 8 degrees duration over a std stroke SB

Personally though I reckon your bigger problem is in your heads - if you want to "go deep" into the 12s...., you really need around 250cfm peak to match a cam that will work to 6000 rpm in that build.

I'd doubt your making peak HP much past 5000 with that combo unfortunately.

Whats your shift point?

FWIW, I have a very similar build with heads that flow 243@ .550, i run a 245/252 duration cam with .520/.540 lift, same 3.89 gears as you and a fatter 3650 lb car.

My best is 12.3 at 111mph - with a very ordinary 60ft.

Your MPH is way low and its the heads and cam thats doing it IMHO.