CobraGreen
The stick will be more fun to drive, but I am sorry to see you wasted your money on the C4. I hope you can sell it and get back some of your investment. You might be able to sell the 351W heads too and the 289 heads if you decide not to use them.
My car runs in the high 12s and I think yours could too with not too much effort. It would be a good idea to have a total package that is matched up well. I did my car in stages.
Your car needs to be able to put the power to the ground. This is why I recommended tires. This is a link to where I bought my recent pair of G6015 American Racers. Enter the word tire in the search box and it will direct you to these tires. They cost less from this vender than from Powered by Ford where I bought my first set. I think shipping was less expensive too. This is the link:
http://www.parts123.com/PartFrame.a...stmotorsportsinc.com&TITLE=Midwest_Motorsport
I think that your engine with proper heads, cam, intake, exhaust and gears could run better than my car, especially since your car is carburated and probably weighs less than mine.
What year t5 are you putting in the car? My car was a 90 and has an 8 tooth drive gear on the output shaft of the trans. If your trans is an 89 or earlier you have a 7 tooth gear. The Ford Motorsport catalog lists the correct speedo gears for different ratios. A red driven gear on the 8 tooth drive gear is accurate for 3.27 gears. A red gear on the 7 tooth drive gear is accurate for 3.73 gears. Ford also sells a six tooth drive gear which would be handy if you are running 3.90, 4.10, or 4.30 gears.
I bought my Summit long tubes because they are affordable and I beleive they make more power than a shorty header.
I think your 80 could run 12s if you put on ported 289 heads or ported GT40s or stock aluminum heads, a larger hydraulic cam like the Comp Cam Extreme Energy XE268H or XE274H, a performer RPM, the Summit long tubes, and a 3.55 or 3.73 TurboCoupe rear end with the G6015 American Racer tires. It might go 12s with unported 289 heads or unported GT40ps or GT40s, but porting would be better. Some guys put Chevy 1.94 /1.60 valves in the 289 heads. A set of GT40ps might be cheaper than modifying your 289 heads. Here is a link about 1/2 way down page to some assembled GT40ps that are ported on the exhaust side:
http://www.foxlakesale.quartermilemuscle.com/
You might need to check piston to valve clearance if you run larger valves. It is up to you if you think it is worth putting money in the 289 heads. I bought my complete "stage 2 ported" iron GT40 iron heads with 1.6 rockers for $600 used. I think it might cost more than that to do you 289 heads unless you can get a deal on the machine work. I don't have flow numbers from the stage 2 porting, but the bowls are ported and both the intake and exhaust ports are opened up to match gaskets. Good luck and keep us informed. Tom