man just get the o-ring seals and the cylinder base o-ring or gasket, don't be cheap and it's not worth taking the chance that your old ones will work ok. they won't, they've been compressed for how long.
For the exhaust nuts, try heating them with a heat gun before removal. If you cannt get them loose then you'll have to split them, w/ a hack saw and ordremal w/ a cutoff wheel. Cut most of the way through then split w/ a chisel. the reason you'll stop just shy of cutting all the way through w/ a hack saw is to stay away from the exhast threads on the head. A chisel will bust the nut and allow it to be removed..
Hopefully you won't have to do this. Check the threads on the head as you don't want to cross thread, if threads are a little buggered up then you'll need to chase w/ a thread file.
When putting exhaust nuts back on, coat the threads w/ anti seize.