Exhaust opinion

I am swapping the 318 in my 87 D150 to a 360.I have Hedman coated long tube headers for it and am debating whether to run a 3" single exhaust or a dual 2.5 exhaust.I have mufflers and pipe for both applications.I am leaning towards the 3" single for a factory look.
My questions are would the 3" single lose appreciable power(engine is mild 360 that I hope makes 350hp) vs. the dual setup?

If I go with the single is it worthwhile to do an H or X pipe before they merge into one pipe?



The motor is an 84 reman longblock that will have some light headwork,cam(at this point something similar to a comp xe262 or the like),performer intake and a 4 barrel in the 650-750 range as I have several extras.The block will be decked and the heads shaved to get me as close to 9.00-1 as possible.This is what I have to work with.

It has the stock gearing which is unknown at this point but will likely end up in the 3.23/3.55 range with a sure grip added.

Not a hot rod or heavy project just want a dependable truck that can get out of its own way if needed.I bought it for a $1000 with a 318 with a cracked block.