Here's what I ended up doing...
1) Drilled the hole for the neg post and attached the post using a screw. Nothing tricky.
2) Poured in a layer of JB-Weld, just thick enough to cover the neg Boston screw head.
3) Once the JBW had cured, I drilled out the holes for the pos posts... Holes were just wide enough to get the posts
through.
4) used a slightly larger bit to drill out the steel deck to make sure there was total isolation between the deck and the posts.
5) Drilled 3 holes in a thick brass washer. Two for the dual pos posts and one for the the screw head pos contact.
6) Ground it down so that could sit flat on the 1st layer of JBW w/o touching the walls of the tube.
7) Once I had the pos posts ground down to the correct length, I attached them to the plate w brass screws. Also squirted in a little solder paste, top and bottom.
8) Used a soldering iron to reflow the solder paste, creating a VERY solid connection between the plate, screws and posts.
9) Ground the heads off the screws so that they'd be out of the way.
10) Tapped the 3rd hole to accept a 4/40 brass screw.
11) Attached a 4/40 nut and screw, to mask off the area and provide a handle for getting everything situated.
12) Potted the pos post assembly in a 2nd layer of JBW, filling it up to the top of the nut (but not covering it).
13) Once the 2nd layer of JBW was dry, I used an X-Acto knife to cut around the nut and backed off the screw enough to rock nut out of it's place.
14) Cut the screw down to about 3mm and reinserted it into the pos plate.
