OK, here are some pics and numbers...
Here is a shot of the intake runner openings where they would bolt up to the IMRCs...
Side shot of intake...
Measuring ID of runners...
I concluded after several measurements the ID of the runners to be 31mm.
They measure a bit funny the other direction because of the oblique angle to the face of the intake...
Note the different lengths of the primary and secondary runners...
Also note how the shorter runners tuck under the longer runners...
To get access to measure the length of the runners, I removed one of the blowout plugs in the bottom of the plenum...
Using a piece of small diameter poly rope with a couple o-rings slid onto it for movable markers, I was able to determine the length of the runners. The short runner inside length measured 6.75 inches (172mm) and the long runner inside length measured 9.125" (232mm). Note these lengths are along the inside edge of the runner(s).
The OD of the runner tubes pretty much measured 35mm...
With an ID of 31mm and an OD of 35mm, the wall thickness is approximately 2mm which is pretty thin for anyone thinking about porting the intake...
I may later cut the plenum apart and rig up a jig to measure the runner volumes but this should give enough info for what is needed for now.
I hope this helps.