As far as I know the only upgrade available to a CA smog truck is the LS conversion kit available from GM.
The E-Rod LS or LT setups are CARB approved aftermarket parts for any pre 1996 vehicle, there are a few additional requirements that need to be done when swapping too though.
You can swap in any drive train from a newer vehicle so long as it meets the rules below (and more)
I was about half way through swapping in the 1998 350 vortec when I figured out getting the correct factory computer wasn't practical & the cats were going to cost about $1200... I just gave up at that point but it could have been finished legally.
I believe if you have an entire donor, say a 2002 k1500, and transfer every single piece you can get that to pass the referee. I may be wrong…
Yes and no...
The donor vehicle type must be classified the same as the receiving vehicle, Ex 1/2 ton pickup to K10, SUV to K5, ETC.
(Note: I cant LS swap my 2018 jeep even under fed standards because LS's were not available in SUV's in 2018, it would have to be an LT type engine)
The donor vehicle must have been a CA smog designated vehicle
The receiving vehicle must be in CA approved SMOG configuration when complete even if it was originally a federal smog vehicle.
The factory ECM must be unmolested in regard to CEL/MIL and smog functions but VATS and other stuff can be disabled. (My ECM thinks it is in a Chevy Express van with a 5.7L & 4L60E trans, which goes against the top rule)
The factory TCM must be unmolested and work as designed, if the donor had an electronic assisted trans it needs to be part of the swap
CEL/MIL needs to function and be visible from the drivers seat
The receiving vehicle needs to have all of the same equipment (or CARB approved aftermarket parts designed for the donor vehicle) as the donor except gas tanks, but the existing tank must accept all the modern sensors or equipment and pass the same pressure, purge & evap tests.
Cat's must be CARB approved and be in the same configuration and be the same distance from the manifold within a few inches
O2 sensors must be in the same configuration and the same distance from the manifold within a few inches
There's pages worth of CA Bureau of Automotive Repair and CARB engine swap guidelines I am forgetting but that is the meat & potato's of it.