Chevy Venture 3.4l Replacing Rod Bearing

Is it possible to replace a rod bearing in a 2000 Chevrolet Venture without dropping the engine and transmission from the van? I just finished replacing the intake manifold gasket - which apparently caused the rod bearing to wear out, and I want to avoid pulling the top end of the engine apart if at all possible

Yes, it’s possible.
However, the new bearings may not last long. It all depends on if the crank journal is scored, worn beyond specs, etc.
The only way to determine if the crank is beyond specs is by carefully using a micrometer to measure journal roundness, taper, etc. and even then it’s a good idea to check the oil clearance with Plastigage.

Wonderful! I take it that if the crank is beyond specs It will need to be replaced. The knock isn’t so bad, it only occurs on acceleration and release of the throttle when the engine returns to idle. I know I can get undersized bearings up to 1.00mm, but nothing oversized.
I will need to remove the motor mount below the crank pully and support the engine from above if I’m not mistaken. I have the Haynes manual but it seems to leave out some steps.