Mill .0048 for every 1 cc on a 360 head, .0053 for every cc on a 318 head.
Head Milling vs.
Have you done a cranking psi test yet?
What were the results?
Those sound like they either have small 360 valves in them or you have a set of 360 heads.
The open chamber 318 heads come out to around 68cc
The open chamber 360 heads come out to around 72cc
If using the 72cc 360 heads, removing 8 cc's would be what I would do.
BUT I would also cc the heads 1st to be sure....then determine the amount to mill.
Start with finding the cast number of the heads, then report back.