Why not set up a overdrive box off your t-case instead of going with a 6 speed? This would give you the same low granny gear for crawling, but would raise it for high way. One of my dad's fiends had it done in an FJ60 back in the day. Put 65 mph down to 2500 rpm. Not sure of the ratio since...
Gorgeous Cruiser. My dad bought an '82 in '87. He sold it when I was 7. I wasn't too happy about that and bought my own '82 when I was 16. 6 months into it, a drunk driver ran me off the road and I rolled... Hoping I can get another after I graduate. Looking at a HJ61 when they're legal to...
If it's coming from your rear heater, it's probably a pinhole in the coolant tubes inside the heater unit itself... I had this happen to me last winter.
P.S. If I wasn't a broke senior in High School, I'd definitely be over there looking to put my FJ60's axels, tranny and t-case in it. Don't Part out your Cruiser. It's in too good of shape for that. Have you tried craigslist? I'd imagine with winter bringing the slick roads that some skier...