Front mount turbo such as On3 or Huron Speed. Both are budget friendly options. We did a Firehawk with a On3 78/75 and made over 560 on 14psi on our Mustang Dyno.

i had a 02 ws6 with a sts rear mount. on 12psi on a stock 5.3 other than a cam it made 575rwhp and 612tq. it was fun but even with he precision 6776 turbo it had to much lag for me.
it was fun for the street but useless in a race. by the time you are in your power band even with a cam you are shifting again.

480 to the wheels and only went low 12s? On DRs?

May have been stock stall at the time. like 12.1 @ 127ish I think

I would do LT's, a converter and gears in thet blue droptop.

Fast enough to put a smile on your face and get booted from the track without a bar.