3 speed manual and 2.76 gears with /6

An auto changes the whole thing.... the torque converter slippage and torque multiplication makes it NORMAL to use a significantly lower rear gear than a manual. If you are not towing or hauling and are not wanting the maximal off-the-line performance, then down at 3.00 or less is the way I would go. 2700 RPM calculated will be actually be more like 2800-2900 rpm with a non-locking torque converter, and even 2700 will be a noisy RPM at 70-75 mph on the interstate. I have a '62 B-body Dart with /6 that has a 3.31 rear and 3 speed manual and it is not a comfortable interstate crusier with the RPM's up around 2700.

And as far as performance.... I had a '70 Ranchero with a warmed up 351C (set up as a good breather but cammed and carbed for low end torque), C4 trannie, stock converter and 3.00 rear axle and it would beat 440 B-Bodies and 340 A-bodies all day long. It was fun to have the 1-2 shift up a 55 MPH and the 2-3 shift up at 85 MPH! So you can have plenty of grin factor if you go with that 360 and keep a 3.00 rear axle for good interstate crusing.