1965 mopar 273 heads

Yes, the heads will bolt on.

However, I would recommend using the 318 heads as they have smaller combustion chambers so you don't lower your compression too much.

The 340/360 heads have larger combustion chambers which can lower your compression by 1.2 - 1.5 points.

The early 273 heads had smaller combustion chambers, so even putting a 66 318 head will drop the compression a little, but not too bad.

I would find a set of early 66 -69 273/318 heads and have hardened seats put in them, or the 302 later castings as they have reasonable chambers, but I'm not sure how much to keep your compression from dropping...