Can anyone tell me to exhaust pipe diameter of a stock 351M in a '79 F150 Supercab?

Also, if I stick with the single exhaust, what is the recommended diameter I should use? Or if daul, anyone have any ideas? Pictures?

 

I belive it should be 2 1/2 on the Y Pipe to the muffler. Then 2 1/4 coming off the muffler.
I'm running Dual 2 1/2's off my 400 but it's slightly modified. I ran dual 2 1/4's off the stock manifolds on my 78 Bronco and it did well.

 

dual 2 1/2 pipes from my headers into a y-pipe to single 3" pipe into a muffler and out back madrel bent 3" pipe for trail use i use a 3" turn down right after the muffler. flows pretty good. and my 400 is not stock.

 

mine does good with 3' collectors and no pipe

 

On my 78 F150 The exuast is stock and it runs 2.5 in straight from manifolds to tail pipe

 

Wow, I don't even know what stock exhaust on these things would look like.