You've probably yanked the 4runner seats out by now and seen that they're held on by 4 bolts to the frame.
I'd think that, assuming the celica seats are not power, I'd see about adapting the 4runner slide rails to the celica seats.
Maybe you're really lucky and the celica's brackets (the 4 point anchor) are in roughly the same pattern as the 4runner's.
I love my seats, but the lumbar is in exactly the wrong place for me... too high up. But then again I'm 6'4" and most of that is leg. God I wish the wheel telescoped.
Trust me, I'm an engineer.
2002 4Runner 5VZ-FE 61K Limited 4WD
Now: Kenwood CD Head + Custom iPod interface, Pheonix Gold M50 amp + JL 12W0 sub, Mobile 1 synthetic, napa gold oversized filter (FIL1516), ISR mod, running boards = !buhleted!
Sooner: Deckplate, bigger mudders: 32? 33?
Later: 1.5" body lift, 2.5" suspension lift of some variety. (undecided)
SigSauer P229 .40 S&W Equipped!
RIP 1994 4Runner SR5 5spd MT, 31x10.50 Dunlop Mudders, 186K 3VZE blown engine.