flag4runner

I have an 88 4runner, totally love it, but its my daily and i don't want to beat the crap out of it, so i have been looking for a toy. there is a clean-ish 3rd gen that i could get for under 1k, motor runs, but the auto tranny wont go anywhere after it gets warm. Maybe its just a transmission sensor issue? but i honestly hate the automatic with the 3vze and would love to swap it to manual. i even have several manual options picked out at my junkyard that would fit. Would it be worth it to try to put a manual in? and is that totally out of reach for a somewhat novice mechanic?