It depends on the specific header most come out the bottom witht the starter & oil filter removed , some can be remove from the top again with the starter removed , some ahve the center link going through the header so you can remove the center link or cut the header tube .
I agree with rebuilding but you need to tune on the engine , the bad news is this is not going to run well Comp Cams are not great & the combo of a 110* cl & stock manifolds is not going to work well at all .
Part of the real problem with R&P is the Mopar lower ball joint , there is no proper replacement for front steer & putting a rack where the center link is now under the oilpan doesn't help a lot so the simple solution is seems to be to alter the K frame , swap to front steer & use Mustang II /...