what ex gaskets to buy
Manfolds, I think these are B/E body SB manifolds
"SB" doesn't help much. 318? 340/360?
Okay, the reason I'm asking is because of port size. Manifolds made for early 340/360 heads (X, J, O, etc.) have larger exhaust ports than later LA 360 heads/manifolds (587, 594, 308, 408, 409, etc.- anything with a smog-style exhaust port), which are actually closer to 318 sized... Since the port size on a Magnum is also closer to a 318 port size/shape, an early port 340/360 manifold can actually overlap the manifold mounting surface on many Magnum heads, causing chronic exhaust leaks no matter what gasket you use.
More detail and pics here, as well as some solutions:
Magnum Heads On 340
If you have later 360 or even 318 manifolds, it should be no problem. As was already said, Ma Mopar didn't even use exhaust gaskets- in some cases (but not all) they had thin steel shims that served as plug wire shields, yes- but no gaskets. Even on Magnums. So if your manifold and head surfaces are true and flat, you don't need them. Run 'em if you insist, but save the fancy and expensive gaskets for headers.