Looking at some numbers for an 1981 Mirada it says 3501lbs curb for the 5.2V8 version, so if we only add 150lbs for driver = 3650 at the line approx. 110mph is 395 track hp@crank, which is only 30 more than my old stock '71 340 motor made with a Holley strip Dom int./MP.590 solid ft cam and an 850DP, (750DP lost 2/10ths) that ran 12.39@108+ at 3550lbs+, had a 4200stall/4.30's/10x28's and trapped at 6300.

With those tyres/gears your only trapping at around 5000 with slip, not enough. Adding 2.08's and CNC work added hp, but not usable hp with the chassis set up hence the same ET/mph. A Solid ft cam matched to the heads would be better in my opinion, 4.30's and at least a 4200 stall depending on cam choice would be good, it needs to trap at 6000+ and it'll pick up no end, an 850DP could be worth trying if you can borrow 1 and tune it.

As an example I picked up 1 sec and almost 8mph going from a 302track hp set up to 365hp with the spec mentioned above, thats 60hp which is around 4>5 ths, the rest came from going to 4.30's from 3.55's and a 4200stall from a 3500stall, 60ft is ET.

my 2c's.