well what difference is intake manifold is there, as i wasnt to put a 290 on a 260 if its going to increase performance, and want other parts would be good to put in that wont have any drama to be put in, i.e. cams, heads roller rockers, injectors and what increase would any of these have if any. help please even if its just basic or about one or the other

Intakes are not different.
Cams are different, heads the same, pistons are different, rods are different.
Get a whole 290,302,315 engine to do it right.