When I built my bending fixture I made sure the threaded rods cleared the available space in both the AKM and Yugo flats. I had one of the last Tapco Yugo flats on hand.
When AK-Builder came out with their flats I decided to use the Tapco flat for the test build and just ignore all the unwanted underfolder holes.
When I checked the AK-builder flat I ran into a problem - the pistol grip hole was smaller than the 3/8" all-thread, plus it was offset maybe 1/8" from the Tapco. Which means I can't run my pullrod into that hole.
The big hole in the Tapco flat looks just like the one in my Romanian flat. A Romanian grip nut fits. I'm guessing the Tapco one is designed for something riveted on.
Also note the substantial differences in the carrier cutouts and miscellaneous holes.