what crankshaft could i use?

As far as pins go, full floating is preferred. It's easier to dismount and remount if you need to, and there's less of a chance of messing up with pin centering and heating the small end of the rod like apress pin. As far as cranks, I've seen 318 cranks go with 727s and 904s, but I cant swear that "all will work". '68 was the first year of 318s, and I think the cranks are the same thru '71. Later ones will interchange, as I think it's the balance (counterweight size) that varies.