[Jac Mac]

These pics from links on your thread create more questions. In your side view of the alloy block and heads it has the extra head bolts and notice that beside each exh port it has a longer stud ala 351c wheras the pic from link by Mark S has no extra studs and short ( normal ) type SBF outer row of studs.
Re-read chapter in Des Hammill book, it appears that there might have been two or more evolutions of the early pushrod Alloy Indy block, but in saying that the castings of block in your pics have a more 'european' appearance. If you disassembled that block did it have provision for wills & O-rings at deck surface, or just flat for conventional gaskets.