I installed a 1984 SJ410 body on a 1990 frame last year. The front mounts under the headlights and the rear mounts under the tailgate were the same and the six body mounts in the middle were off about an inch or two. I installed a 2" body lift at the same time (so the shorter SJ410 hood cleared the radiator) and was able to use the 2" square tube blocks and drill them out at two different locations (offset) so it would bolt together properly. In this swap I cut out the steel dash and cut the firewall for the 1990 brake booster (the SJ410 had no brake booster). ALso, the shifter hole has to be widened out a tiny bit....just a little. It was a little more work, but not that much harder than a typical body swap.
.....so yes it will fit with a little extra work.
Sean
I found that the height of the rear centre mounts was also different. Did you add spacers?
When you say the 1990 booster do you mean SJ413/Samurai. Over here later Spanish built 410s had boosters but I found that not only were the fixing holes different but the studs were on the other part (firewall/booster, can't remember which was which)
Here are some pics I took at the time of my body and the frame showing the mountings
Crossmember in front of rear axle, IIRC the front outrigger is the correct height but the hole is again a little off:

Centre section, if you look at a sammy you will see that it is straighter and therefore higher
