With the 3.55's I would run the XE 262 or similar.You need torque to move the barge.You could step up to the 268 with 3.91's and be ok also.
I would swap the DP for a 750 vacuum secondary with a quick change secondary kit to tune the secodaries by stiffer/lighter spring.
The 400 will outperform the 360 but you will swap a lot of stuff to get it there.
Consider a spreadbore carb if mileage is a concern.
The snappiest combo would be with the 262 cam and 3.91 gears.Would'nt need a stall and would pull to 5200(ish)rpm with ease.