I think all the head casting numbers are the same and the standard heads were machined to fit stage 1 valves. The actual (catalog) part number for stage one heads ('71) is 1237660. Non stage 1 heads are 1237659. Again, the casting numbers would be different from the part number and the same for std and st1. I'll take a look at the '71 heads I have here and see what casting number is on them.
1238148 heads are 72 and up. Casting numbers will not tell you if they are stage1 or standard and stage1 heads had the same casting number for their year, Most 71 heads that I have seen are 1237661. There were 71/2 heads that had the big valves, but were not unshrouded. Stage1's were unshrouded.
