Will there be any complications with using 1989 L98 heads, all stock except for the springs and studs, and a mild aftermartket hydraulic flat tappet camshaft? Will I need different rockers or guidplates?

 

No problems, just remember to get some pushrods for a non roller cam.

 

Those heads will have press in studs, no problem there. They are set up for self align rockers with the larger holes for the pushrods through the heads so you'll either need to pull studs, thread for screw in rocker studs or just stay with the self align rockers. Still no problem either way. Should work fine. Pretty good small chamber heads.