What type of RPM's are you planning to run? Are you using aftermarket head gaskets? Do you want to use aftermarket head gaskets?
The m38 head is a big improvement in flow over the 30/35, specially when ported correctly with proper valve seat machining and valves. Personally, I don't know what he limits are for the class you race but I do know that I have seen a M38 with a modified VG head turn out 70HP at 8800 rpm.
CRAZY