1980s pickup engine replacement non 20r

Looking for a good replacement for my 1980s 20r. I'm wondering if there is a good replacement with minimal down stream issues.

Obviously I'm not going to gain much in horsepower or torque. But can I get a slight bump without causing other complications in the drive train?

I'm guessing a few thousand tacoma world members know this answer. But most have moved on (I'm late to the rebuild party)

A key component of this.... is that it MUST pass Colorado emissions which are the strictess in the nation's (same as California)

We have decided to not build this into a trailer rock crawler. We want it road legal.

 

https://board.marlincrawler.com/index.php?topic=19275.0

 

Here in NM any vehicle over 35 years old is not required to have an emissions test. You may want to see if it’s similar in Colorado