Once I replaced all of the worn steering linkages and the steering stabilizer, the BJ spacers seem to work fine. However I have had to replace the idler arm once already, but that was also the side I broke the old tie-rod on the trail. I can't comment on the long term wear effects though, my '91 is only a home-to-trail-to home rig, and the occasional trip to town, less than 2k in two years that it has been finished.

With the desire to run 38's you really don't have much of an option but to do an SAS, as well as cut the sheet metal. Adding on a lift kit to try and clear 38's will just make your truck unsafe to drive. To maintain a good center of gravity requires you to increase the track width by 1.5" for every inch of increase in height. If you add 3" suspension lift plus 38's(3.5 more inches of lift) you will have lifted your truck 9.5" which will require you to wide your track width 14"(move each tire out 7"). Absent running full size axles or 16" tires you will have a very unstable rig, both on the street and especially on the trail. You may want to rethink your need to run 38's, the cost of building everything goes up substantially once you move past 35's.

Whatever engine you swap in, you will have to use the ecu that is designed to work w/that engine, not the original one. You then have to wire up the new ecu to work with the oem wiring. What ever engine you swap in, try to get the hole vehicle, so you have everything you need.

The 4.3 is a good swap if you want Chevy power, I like others prefer to keep it all Toyota. When I am done w/my '87 Supra restoration I will likely be putting either a N/A 7m or 2jz(both I6 motors) in my '91. The 7m is about the same HP and but less torque than the N/A 3.4, while the 2j has about 30 more ponies and the same torque as the 3.4.

What will help us give you more input is to answer what are your goals for the truck, what type of wheeling do you do/want to do?