13's shouldn't be much of a problem, I had a low compression LA 360 with a small lunati cam in a 68 4dr dart it ran 13.30s at 104 with 2.76 gears...only run 1st and 2nd gear no need to shift to 3rd. I have no clue what rpm I was shifting or went thru the lights at i didnt have a tach in it and I didn't care. The car was a blast.
Don't take this the wrong way but your idea of a blast and mine are two different things. I will have to see a 13 time slip from the original OP to believe it could run 13's