Rod bearings??

[Schurkey]

can I rebuild the motor

Depends on your skill level, and willingness to get--and keep--things scrupulously clean.

Who would be good to buy a rebuild from

There's a zillion vendors, but consider buying the rebuild kit directly from your machinist.

I also would want to put a mild cam in it for low torque for towing.

The engine already has a mild cam intended for low-rpm torque.

A different cam may or may not require specialized tuning.

I was thinking of the engine tech rebuild kit. but im looking for somthing that will last at least 200k miles

That's going to depend on how you treat the engine, in addition to the quality of the machinework, and the assembly/break-in.

 

[Dan Mark]

Just thought I'd share this video of my truck with a spun bearing.

I know I wasn't sure if that's what it was until I tore the engine down. Maybe it will help the next guy "know" right away.

K1500 Spun Bearing

I purchased another 350 and did a light rebuild and swapped it out.

As others have said, once it's knocking, it's too late. Mine started knocking and I immediately shut it down. The crank shaft was toast.