Not sure to keep this one granny spec or make it a sleeper.
Go beyond sleeper. Std wheels with race rubber and wedge in a late model turbo. You want stealth with this bad boy.
I first became aware of “sleepers” in the eighties while in my late teens. There was a guy prob in his 30s how had what looked like a bog std Ford Mk1 Cortina auto. It had cross plies, std interior, hub caps, std muffler in place with pea shooter chrome tail pipe and so on. Under the bonnet though was a hot 302 Windsor. It certainly did not sound as it looked. I was enamored especially with touches like headers merging into the 3" exhaust that went into the std looking muffler which was an empty can that had some exhuast channled out the pea shooter and the rest through a 3" hole in the bottom. It did like a 13sec 1/4 on cross plies and low 10sec on Hoosiers.
I am thinking a nice fuel injected motor, maybe lower it a bit and a set of 15" steel wheels. I have a set off an Fiesta that we used to own…only issue is they are 4x108 pcd. Trying to work out the best way of making them fit.