Cyl Head info needed !!!

Ok so just tonight I finally pulled valve covers to see what cyl heads my 340 has on it and I found the following casting numbers # 3418915
I also saw 360 on other end of each cyl head so I assume after looking online I have
1971 360 heads .
do these particular heads have performance potential and if so how much with serious porting etc
thanks Chris .
#3418915 is a 71-72 340-360 head open chamber with 1.88/1.60 valves. Cast mark "J".