There is nothing wrong with your torqey Bolt engine. The obstacles to doing 70-80 MPH comfortably are the rear differential, transmission, shocks, tires, brakes and steering. (stopping and steering at 70-80 are as important as actually going 70-80)
The tried and true formula is radial tires, a T-5, new rear diff, disc brakes, dual master, tube shocks, and upgraded tie rod ends. A powerglide and numerically low rear diff gears would work just fine with those other things. (ie 3.08:1)
Ever drive a JEEP CJ, Wrangler or Cherokee?
They've been using the 4.0 liter inline six for 30 years with plenty of success (244 cid). Many of those years involved a t-5. I think a 235 is about 3.85 liters and a 261 is somewhere around 4.3 liters.I've got a '92 cherokee and with the t-5 it is pretty zippy in town, and cruises at 85mph easily.
The nova you got that engine/tranny combo out of was produced when the speed limit on highways was 75 (before it went to 55 under Carter). I have not doubt that you'll have no problem doing 75-80 with the 230/powerglide combo in your AD.
