What Cam would you suggest with this

Guy just wants a cam and you guys want to rebuild his whole car. I 2nd the comp 265deh cam will give you a good bump in power. You could do the custom cam but probably similar in specs anyways.

I wouldn't worry about manifolds under 300-350 hp they don't matter much. I've been looking into cause like you I'm stuck with shitty 273 manifolds. Ive seen two different create 300 hp 360 doing different manifold to header shoot outs and one 500 hp 440 manifolds to headers shoot out.

There was basically 2 hp difference from 318 to 360 and 360 to 340 and 340 to shorty headers and 5 hp between shorty and long tube. 318 manifolds made 311hp and long tube did 321hp im guessing once you reach 350 hp headers start to become mandatory. They didn't do 273 manifolds but there probably same as 318 or at most 2 hp less. Magnum as a set was in between 360 and 340 but they found a combo of one magnum and one 340 was the best pair. In the 440 shoot out the shorty made 50 hp and long tube made 70 hp over.

I wouldn't dig into your engine for more CR unless it also included porting and more cam then it would be worth it. But that could be a down the road mod after you get tired of the decent power bump from the cam.