On your deal if the drivetrain eats up 10 % or more (which most due eat up more) of the HP then the motors is making around 330 HP.
I would install a bigger exhaust system, 3.0 or maybe 3.5 inch from the collectors back on the car first and see if that frees up 20 to 50 HP, NO kidding
The bigger motor will need it and you will probably be pleasantly surprised with the gains in power from idle to WOT
My old 1969 Dart GTS picked up from 12.23 at 109.5 MPH in the 1/4 mile at LACR to 11.39 at 117.6 MPH by removing the 2.5 inch exhaust system which had a set of Thrust Corvair 2.5 inch turbo muffs with 2.5 inch pipes form the collectors to the muffs about 30 inches ands then about 24 inches of 2.5 pipes exiting to the front edge of the rear wheel wells
That motor was a stock bore and stroke 440 motor with a set of TRW pop up pistons with around 11.2 to 1 compression ratio with a set of iron 906 heads that had a little bit of work done on them, no where as good as the heads available today like the 440 Source heads. TM7 intake with a 850 Holley DP carb, small Crane solid roller cam with ductile iron rocker arms, no real all out race parts for that time
That car did end up running 11.17 ET at 122.+ MPH at Las Vegas later that year in November during a cold spell.
My Duster with a 511 C.I. pump gas 400 stroker motor with a 3.0 inch exhaust system picked up .020 ET and .2 MPH in the 1/8 mile by removing the complete exhaust system which exited at the rear bumper I think the weight loss was most of those small gains
That car had a set of Hooker fenderwell 2.0 inch primary pipes with 3.5 inch collectors headers with 3.0 inch pipes straight back under the rocker panels on the side of the car (they hid the ladder bar mounts ) to the Magnaflow 14x7x3.0 in and out oval straight through muffs mounted behind the rear end exiting at the rear bumper