ID THIS BLOCK

According to your information, you have a hydraulic lifter cylinder head. I would not use that, as the slant 6 was not a very good hydraulic lifter engine, IMO.
The head should not make any difference. The difference is in the valve train ( cam, lifters, pushrods, rocker arms, rocker shaft). You can run either head with either valve train. But you must change the "complete" valve train. Also, you must run the correct valve cover for the head used.