This is a helpful article, thanks for posting! Here are my experiences, I'm in the process of replacing the thermostat on my '86 GN.
1) Bought a Stant 160° t-stat; indeed, I had to cut it down with tin snips as it wouldn't fit the hole in the block. I filed it smooth so there were no burrs. The unit I removed was a 180° unit.
2) I had to remove the up pipe, MAF/Turbo pipe; I had a helluva time removing the S hose however, as whomever installed it before positioned the front/lower clamp in such a way that the screw-head was facing directly to the passenger side of the car, instead of up. I had to loosen this to be able to remove the S hose; loosening the upper/block-side clamp wasn't enough for me to pop it off and out of the way of the thermostat housing retaining clip.
3) Once I had the S hose off, I reattached the upper rad hose to the t-stat housing and the housing popped off rather easily just by firmly jiggling the upper hose back & forth.
I decided I didn't want to re-use the original O-ring so I'm picking up a new t-stat housing after work today...I assume they come with the O-ring?
Thanks again for the how-to!