what heads to run on a 273

so i had my block boiled and board out .30 over..stock crank and using
egge dome pistons....

what can i do with the heads? i need bigger ports..does anyone know of a good flowing head out there for this little beast?..

i would prefer to use my the heads and cut cost but whats the biggest valve i can run? what to port them out to?do 318 heads fit on these 273??

thanks fabo!!:D