so you have the head off good time to have it resurfaced if needed and replace vavle stem and jet vavle seals
and alway good to check and make sure exhaust manifold is straight. they like to warp and is hell to get them to seal and not blow exhaust gasket.
of course there are numerous other things that could be done.
new silent shaft chain and gears and guides .
but then it all depends on what you have done already and how everything looks

owned a few .. current 86 rustbucket 2.5td . manual hubs