The 9.25 with the 3.55s and Suregrip is the easiest. By this I mean unbolt your current rear axle, bolt in the new axle. The driveshaft length will be the same, the 8.25 and 9.25 were the same distance between axle centerline and U-joint.

There's no reason to even smell gear oil on this swap. It's just remove and replace. Well, you will have to bleed the rear brakes, but nothing more complicated than that.

As for the intake, you have many choices. The LD4b is good, the LD340 or RPM Air Gap would be good, the Performer would be good, even the stock cast iron spreadbore intake that was used on 360s is good, if heavy.
Get a carb that matches the flange on the intake. I have had middling results with square to spread adapters.
Don't worry about the port mismatch, at this power level it has no effect. Just use a gasket that will seal whichever larger holes you have. I guess that'd be a 360 gasket.

Even with the wimpy 318 cam the 4 barrel and dual exhaust will help a lot, even better with 3.55s.

Keep it simple and you'll have success.

R.