What to do...
This pretty much lays to rest your doubts on the performance and mpg debate.
I would do a V8 smallblock transplant unless you REALLY want the /6.
No you won't;
I ran this set up for 28K miles from 00 to 05.
I then swapped in a 360 in 05. I have 38K on the 360 now and my only regret is I didn't do it sooner.
I gave up about 1.5 mpg; 19ish around town with the \6 to 17.5 with the 360 and one mpg on the hiway 21-22 with the 360. BUT, I gained about 180 HP from ~190 to ~370.
This pretty much lays to rest your doubts on the performance and mpg debate.
I would do a V8 smallblock transplant unless you REALLY want the /6.