I would inspect the vortec, remove belt and see if grinding is still there. or the flex plate, cover, starter nose. Don't take their word for it.
you could use the tbi short block with the vortec intake and heads if they are sound. Make more power with vortec heads on average
I definitely plan on inspecting and finding the real issue first. That is the reason I have a good running TBI motor with 135K miles in a van when the PO said the motor was shot...Vortec engjne has a crank sensor on the timing cover . And as said the heads up . It can be done but to what point do you just find a vortec engine and drop it in and go .
I would also expect I need a different computer than the one that controls the 4L80E?Just need to use the loom and computer for tbi, change to tbi fuel pump and add an inline filter. Should be much easier then ls swap in place of gen 1