[Blowd]

was that based on the Iron Duke- really the last true Pontiac engine

While there is some debate on the Duke being a Chevy II motor or a Pontiac motor, The Pontiac received a cross flow head and became the corporate Tech 4 motor. This is the engine that became the "basis" for the Superduty 4 program. IMSA required basic components to be "interchangeable" with production pieces. There were a lot of variations on the Tech 4, but "R" engines and RWD seem to have the most in common. (don't quote me on the details).
The Superduty 4 parts are strictly race bread. I have one of the later blocks which had features such as: 5 [roller] cam bearings, 3/4" deck and main webs, semi siamesed cylinders, and deep head bolt bosses to name a few. The crank I have is 4130, fully counterweighted, [semi] knife edged, 3.625 stroke, with a Pontiac part number. No coincidence that John Callies was heading up Pontiac Performance at the time. Heads began with cast iron units that flowed 80% better than production counterparts, later developing into "433" and "801" (known by the last 3 digits of the GM part number)aluminum castings from Brodix. And finally the Coswoth DB head you see above. Brodix also made an aluminum SD block that was available through GM.
There are much better and more detailed resources available on this engine, but that's the Cliff Notes...
I'll try to get some photos of the block and crank up here later.