Nope, the cylinder sleeves won't accept the overbore. And if I'm not mistaken, the 4ZE1 2.6 has a longer-stroke crankshaft as well. I guess you could swap-in a 2.6 and run it carb'd, but that's a lot of work too.
I had good luck with the old 2.3 in my '86 Trooper by upgrading the cam and going to a free-flowing turbo muffler. The factory muffler is quiet but also restrictive.
The Jerry Cam in a 2.3 will really perk that ol' engine up. It'll have more of an effect than it does in the larger displacement 2.6.
Other ZuZu Dudes have installed an aftermarket Weber progressive 2-bbl carb for a bit more performance. The Weber 32/36 IIRC.
Weber also makes a non-progressive carb, i.e. both barrels are the same size (38mm). So that would flow more air than the 32/36 carb. You can do a search here on "2.3 Weber" for a lot of posts for that mod.
There are numerous opinions on pros and cons of a header, I'll leave that for you to dig into the old threads. Or maybe another "2.3 pickup Dude" can chime in. You'll find a few different models on eBay and usually the prices are better there.
Jerry Lemond is selling the specially-ground "Jerry Cam" and you can get hold of him by sending a Private Message here (his username is JLEMOND ). Use a larger font in deference to his Old Eyes. Jerry is the ZuZu Guru above all ZuZu Gurus, having worked for the company.
Or drop him a line at [email protected]
and if he ain't too busy he'll get right back to you.
p.s. Welcome to the Planet!!