What came with a 351 4v

Well, there were no factory 302/351 heads that were 4 valve. I have a feeling you mean 4 barrel through. Well, the only difference between 2v and 4v heads on the early Mustangs was the K-code engines(hipo 289 and I believe 302 starting in '68) had screw-in rocker studs. As far as I know the ports and valves were the same. The latter half of the '60s and the early '70s were really it for any performance Windsor parts from the factory, and none were really special at that(unless you count Boss 302 heads, but those arent exactly bolt-on....or practical). Try the Classic Mustang forum. They live and breathe this stuff.

IMO you would be better off getting some GT-40 or GT-40P heads and putting them on a decent shortblock.

Good choice on the car. My first/previous was a '65 coupe as well. My screen name may hint at it just a tad.

The "V" in 2V and 4V stands for venturi aka barrels. So the 351 4V is a 4bbl carb engine. Took me a while to understand this when I was younger. So there ya go. Also I've heard that the only 351 heads worthwhile were the ones produced in the late 60's early 70's. I'd try posting this thread in the classic forum I'm sure some guys on there can shine more light on this topic. Good luck.