get a new chain and sprockets first.. then get some reeds I would get the 4's since you would buy new anyway.. I would get a head and some domes and the timing plate just do it all at once and be done with it..
chain and sprockets $100-$150
reeds $220
head domes $200-250
timing plate 20-50
im just guessing at the prices but they should be ballpark
then if you still want more your into motor mods