Having trouble staying on!

[easymmkay240sx]

Okay, just bought an '89 S13 with 135k miles on the odo. The engine starts and runs but in order to keep it running you have to keep giving it a bit of gas, revs are bouncing off at 2.5k RPM (I had to drive this thing home 16 miles, in bumper to bumper traffic, just imagine the looks I got from people )

Anyways the guy said it just needed some headwork(Although I don't trust this guy's mechanical 'prowess' as he didn't even know that it had all disc brakes)

He included another motor that he says he bought from someone on NICO who did an SR swap up in Austin or Houston and if I have to I'll just swap it in, or if it's just the head, I'll swap that over.