Got a 2000 gmc Sonoma 4.3 . Rod bearings went to shit . Is it honestly worth the time replacing them ? And how would one go about a 350 4 bolt main swap ?

There's a variety of factors that can/ will determine whether an exercise is "worth it" or not. As far as swaps go, you might check out this link - there's boatloads of great info there. Swapping? Heres A List Of Parts And Answered Questions!

 

If you go that route may I suggest an L31 Vortec engine this makes a swap much less

How to swap a Vortec 350 into a 4.3 S10/Sonoma

Doing a little write-up while it is fresh on my mind. This will be specific to 2000-2003 s10 with the 0411 silver computer and 2wd......but a lot of info will cross over into other years. First, the engine: You want 1996-2003 350 out of a full-size truck or an express/savanna van. If it is out...

www.s10forum.com

 

350 4 bolt main swap ?

so you have a 2 bolt main now and want to add 4 bolt main caps? stock or splayed?

 

On a SBC 4 bolt mains are overrated. Put together correctly a 2 bolt would be nearly as strong. Unless you are building that engine for high rpms. In which case an LS with it's 6 bolt mains is the way to go. But installing one in an S10 is more costly and time consuming than the above mentioned L31. They did make s few with 4 bolts, but are rare and only came in 1 tons IIRC.
Another possibility if you have $ to burn:

Dart 31161211 Special High Performance Chevy Block, 4.125 Inch Bore

www.speedwaymotors.com