Well in this case pick the biggest engine the lowest gears and as stock as possible for the long block. To cruise 85 will take 2.45s; so get those from a Fifth Ave. Run the tallest tires you can fit and the A998, also from the 5th will get you off the line reasonably well. I'd run a 360 or a 5.9 Magnum preferred cuz it will have the torque to pull this off.
Say the 360 makes 140ftlbs at 2800; 140 x 2.74 x 2.45=940 which is pretty close to the magic 1000. So now you have take-off, and can cruise 85=2600 with 27s. The 360 needs duals and a 4bbl but not much else. And a bonus is the 8/1 compression LA will burn anything. While the Magnum will make a bit more power to pass, hitting about 3200 at 65 in second gear. Horray for TM.
If you've never cruised your car at 65=2000, well you're in for a treat. Well except for the windnoise lol.
If fuel mileage is important to you, then run the 273 with an A500 and 3.55s. This will get you the same final drive of 2.45, yet the 3.55 x 2.74 x 120of the hi-stalled 273 will catapult you into next Tuesday with a starter of 1167 ftlbs. This will also cruise at 85 = 2600 with 27s. I have tuned stock 2bbl 273s to get very high 20s IMP, so say 24mpgUS, and it wasn't hard.That will get you close to 300miles per tank,give or take. Add a 4bbl and free-flow exhaust and you could be looking at 1362 ftlbs Which is well able to spin 245s. Maybe even 275s,lol.
The vehicle that provides the A500 could be an early Dakota 2wd, and might have a 3.91rear gear. That rear can be made to fit your car A-body relatively easily. This will up the cruise rpm to 85=2850, but those gears will allow you to run the273 as a 2bbl single exhaust and the stock A-500TC. I'll guess this comb could make 110 x 3.91 x 2.74=1178ftlbs on the start-line. So now you're down to finding a suitable donor vehicle. The A-500 will not drop into an early-A, and a later-A needs a bit of tunnel/cross-member work. But Let me tell you; those 3.91s will really wake your 273 up. She'll have a whole new personality.
I think I actually would like this combo for myself. Well, I know I would, cuz I ran my 318 with a 10.96 starter gear a time or two, and a final drive of 1.97,lol, with a stick, and it was awesome. The 273 would have been icing-on-the-cake, in the drive-past-the-pump department.
