The AIH is(99% SURE) 1/2 NPT. I looked all over at the big stores, no luck, I went to a place that bends tube/custom Hyd. lines/ all kinds of brass fittings. You can get just a plug or you can get a plug thing(I don't know what they are called) that has a threaded hole thru the plug and get a fitting to attach your tube for a boost line. I got it for $4 at the supply house. I was surprised how big the AIH is, its like a roll of quarters.
I have no idea about the thermostat.
heard the crossover lines are a waste of $, no personal exp.
If you're doing mods like that, can't hurt to do the CCV mod, it'll keep your IC boots clean at least