318 to 360
I ran a 14.57 at 96.55mph in my 71 Duster with a 360/727 w stock converter/3.23 gear. It was a mid 80s 360 from a van. It got a cheapo ball hone/rering job and fresh bearings.
I got my mount from Schumachers, but I've also cut and welded a 318 one to work too.
All I added was an alum intake with 650 carb, a MP cam that is only a little bigger than the stock 340. I used 340 exh manifolds and a full 2.5"exhaust.
I used a B & M balanced flex plate from Summit so I didn't have to swap out converters, but for only a little more you could get a converter with a better stall.
Don't use the cam unless you get fresh lifters and do the cam breakin procedure again.
If the exhaust ports have the Emissions passages just run a tap in there and plug them with some hardware store allen screws. I also did a halfass gasket match to open up the exh ports a little.