Is the original Factory 2-in 1-out 914/6 muffler the same as that used on '69-'73 911's ?

Ah, yes!

I thought the original 6 mufflers were actually tucked up a little closer to the body?

I know the 911 mufflers fit, but I thought they were slightly different.

tips exit in a different place (ever so slightly) if i recall correctly...

correct the tail pipe angle is different, and you can make one work by heating and bending the pipe or removing the rear valance!!!

Or by switching to the 72+ 914 rear valence; evidently the "notch" in that is in the correct place for the 911 muffler's tailpipe!

--DD