To make them competitive? At bare minimum cam and head. If your doing it yourself (if your able) then reasonably affordable. I would just do a basic rebuild and buy a already blueprinted head with three angle valve job, degree new cam, reset valves, and let it eat. Keep in mind if the cam doesnt profile right (centerlines) then your going to need a means to twist crank gear or a couple cranks to try and make the numbers work. Might get away with around $175-$200 in each of them. If your unable to do it yourself then I'd estimate a builder to do an update with rebuild is gonna be minimum $400-$500+. Even though they haven't been ran since rebuilt your still looking at a full rebuild to disassemble, replace and profile cam, replace head, etc.