Which tranny to use
 

I have a SBC with apprx. 500HP maybe 600 with or more with NOS in a 68 camaro. I plan on driving it on the street but also plan on trying my hand at the local track in the 1/4 mile.
Right now i have a T350 tranny and a 2000 stall (the stall is probably not enough i know) A freind has a Powerglide and would trade me straight accross.

Which one will be better for me?

Is the T350 that you have now built for 600hp.
How much does your car weigh if you dont know the weight does it have all three seats.

I dont know how much it weighs, i am guessing somewhere in the 3000lb range and yes it has all 3 seats.
As far as the tranny goes i dont think it is built all that fancy but has been gone though.

This is JMO but 600hp on the juice is pushing it a bit for the trans if it don't have all the good stuff in it. I had a all stock body 68 like yourself and it went 3375lb with me in it and I go 180lb. P/G's like a light car best around 3000 or less. If I was going to do more street then strip I would stay with what I had get a 3500 stall and a sportsman brake put in it and have fun. As I said before its JMO. I had the very same set up that I just told you and went 11.79 in the 1/4.

What is a sportsman brake?

A non pro tree trans brake.

I would recomend the powerglide swap, even in stock form they are pretty stout units especially the ones w/ the 1.76 plantaries. If built right a glide can with stand up to 2000 Hp or more depending on internals.
Only down side would be that you'll need more gear with a glide verses a three speed. Also a glide is a much more consistent tranny for bracket racing becuase it only shifts one time.
Less variables = more consistency = winning.
Goodluck, Charles