Another vote for gears. Anything short of swapping in a supra I-6, wont get you the performance that the gears will. You should be able to find 3rd members with 4.56's or 4.88's far cheaper than most bolt on performance pieces, even if you have to have them shipped in from the U.S.

Do the '86's over there have a straight axle up front or the IFS like the ones stateside?

More than tread lightly. Leave it like you were never there, nor anyone else.
'90 X-cab 4.88's 33 BFG AT's, rr ARB, Headers, Ignition upgrade, cold air induction.
'91 X-cab 5.29's 315's BFG MT's, rr ARB, custom bumper and flatbed