Hi George - Thanks for the assist. Here's my first measurement:

Across the face of the bellhousing, from the outside of the hole for the clutch cable (next to starter), measuring almost right over the top of the input shaft to the outside of the mounting hole there. 15 5/8". Let me know if that doesn't make sense. Feel free to counter with a measurement of your own as well!

My comment about the shifter was not a question as to whether the long mount shifter would work, as I can tell it does, because the M410 I have came with a long shifter mounted already. I just thought I read that 164s did not come with the long mount shifter M410, so I was getting my hopes up that it may have not come from one.