I used SR5 seats out of a 2000 4runner in my 1985.
The rear mounting brackets will line up and bolt right in but the front ones will need to be cut off. I cut the old front brackets off and welded them to the track where they needed to be. Not a hard swap, just a few hours.
Damn. Sorry for your loss man, and that's coming from a firefighter who has put out dozens of car/truck fires.
I just bought a 1985 4runner myself a few months ago, and had it trailered home.
I used a donor set of rear belts from a '99 Isuzu Trooper for my '85 4Runner. Going to make a few adjustments, but they work & the kids can now ride safely in the back seat.
http://www.toyota-4runner.org/attachment.php?attachmentid=179494&stc=1&d=1447046484