Ok, after getting validation on the "make it bottom out" plan, I went back to work and took another look at it. Somehow I missed that the base was open all the way through. The weld area inside interfered a little but I only got another 1/4" after cleaning it up. However, I could look up inside from the bottom and see that the tube was stopping where it hit the curved wall of the down-tube. Duh! Progressively trimming the bottom of the stick allowed me to get about 1-5/8" into the base. By the way, my sticks came with about 2" exposed (no powder coat), so I still have an exposed ring of a little more than 1/2" that I will have to deal with.
Now, onto the wiring run. Yes, I can trim the bottom of the stick so that wires can pass through to the base. But I'm not going to, for two reasons. First, my bundle is too large for me to feel comfortable passing between the two pushrod connections, even with anti-chafe. Second, as Aerhed pointed out, the place I do need to drill is at the top of the curved section and I can't get a straight shot at it due to the top tube. I could get a small hole up there and then enlarge it with a die grinder but that's more work than I want to do or am comfortable with (I don't want to mess with the weld). I'm going to route out the bottom of the straight section and outside along the curved part and make a nice cover for it instead.
And, Bill, I took your advice. That slowed things down because as soon as I had a stick and a seat, work stopped while airplane noises ensued. But it didn't really make much difference because the panel clearance was the critical issue (and, yes, I will have to cut the straight tube down to about 3"). However, having the seat in will aid in 'clocking' the grip and, besides, it was fun - so it wasn't a waste.
Thanks again to everyone who replied; it was a big help.