You need your spindle to look exactly like the picture above. The spindle will turn as it meshes with the gear on the crank. For a starting point, you are lining up the dot on the oil pump with the dot on the spindle? I don’t mean to be condescending, I just don’t know your skill level and how much you know about these engines.
The easiest swap would be a z24. I believe that they started using those starting in ‘83. You can use the z24i but there some things that have to be changed in order to stick with the carburetor. I’m not sure of what all needs to be changed aside from the carburetor and intake. Of course the problem is finding a used engine in good shape.
Sounds like something in the trucks wiring causing the issues, whether it’s killing the new parts or making it work intermittently. And, of course, just because something is new doesn’t mean it’s good.
So it’s like new cars these days. Just to replace the spark plugs in my wife’s car takes 2-3 hours because of all the stuff you have to get out of the way first. Glad it was a relatively easy fix for you.
Never had any real problems with the Weber on my ‘85. It’s been on there since I bought the truck almost 20 years ago. It sounds like, for one reason or another, you’re getting trash in your carburetor.