I would try to find an 85 TPI if i was you.
I had an 83 trans am cross fire..After adding a compu-cam,headers,ported intake etc,it was still a slow dog.I then changed it to carberator,Edelbrock performer package,it was actually slower,less torque so i had to add 3:73 gears to compinsate.
The first thing you'll probably have to do is the trans rebuild,thats a grand to start...Not sure if the 84 had the dana 4 x 3 trans,you do not want that trans in your car period..
Quik,not even.....heres some numbers from road and track road tests..give or take a tenth..
84 vette............................................0 to 60 6.7 ....1/4 mile 15.7...sad...
85 vette..TPI......................................0 to 60 5.7.....1/4 mile 14.1..........
04 honda prelude.................................0 to 60 5.9.....1/4 mile 14.5..........
92 honda prelude.................................0 to 60 7.8.....1/4 mile 15.9..........
98 ford escort ....................................0 to 60 7.1.....1/4 mile 15.7 .........
92 Izuzu impulse..................................0 to 60 7.7.....1/4 mile 15.8..........
Those "other" cars are some serious beaters,theres alot of honda on that road and track road test list that will beat the 84,all the 94 to 2000 preludes run 15.1 in the 1/4 mile.Notice the vette has a little better 0 to 60..that means those beaters have more top end and would be pulling up on you after 60 mph.Notice the 85 will run 14.1..Thats what the 99 Mustang GT runs...
Just some stuff to think about,a guy i know out here got a decent 85 TPI for $1500 ...it runs as a daily driver right now...
I would pass and look for an 85...