Center Section Differential Recommendation

Assuming an overdrive 5 or 6 speed stick, I would recommend a clutch suregrip, with 3.73 or 3.91 gears, in a 489 case.
It will accelerate great with your 360/727, but probably have more rpm on the highway than you will like.
The $1320 center section will be what you need, the other is just an empty case. I would call Dr Diff about your needs. He's a good guy, and LOTS of members here recommend him.