This is the exact setup that I'm currently running. However, I'll be getting rid of all my SBC stuff soon, as I have an LS1 sitting in the garage, waiting for a 6 speed .
I'll have to check for sure, but my RPMs are roughly 3K going 60 down the highway. Granted this is on a 24" tire. When I get my 26's on there, it will help a bit. The car is a blast to drive though. If you HAVE to have overdrive, (would be nice), you can always go for a 700R4, which is the older, non-electronic version of the 4L60e. These aren't quite as tough as TH350, but they are reliable, and fairly cheap to rebuild, if need be.
The thing I love the most about SBC stuff is it is DIRT cheap. Cams and valvetrain cost literally 1/5 of what LS based stuff is, which is where I came from. However, the LS is very reliable, and they can be had for very little $$. I know that locally I can pick up a 5.3 from a junkyard for $400 with accessories, intake to pan, that will make just as good of power as an ol 350, and be 10x as reliable. Then there is the issue of tuning, and wiring.
If you have any more questions, LMK!