Really you are asking 2 questions:
1) what engine should I put (or have put) in my rig? and
2) How do I get it through smog?
1) In CA, as far as I have read, you can put almost any passenger car or light truck engine in your GWag as long as it is the same year or newer as your GWag. So, if you want to install a 2005 GM 5.3liter V8 in your 1986 GWag, that could be legal. You must retain all the original smog equipment and configuration of the vehicle it came from. So, if they 2005 GM vehicle had a catalytic converter, EGR, and carbon canister, you have to bring those over to your GWag. If your transmission is stock, then an AMC 360 would be the easiest and most cost effective engine to get your GWag on the road. Yes, if the trans is stock, AMC 360 bolts up. Once you post some pics of your current configuration (engine, transmission, transfer case) we can better help you with your options.
2) If you do an engine swap and it is the same year or newer, and you retain all the original smog equipment, then you take it to a smog referee and they will inspect it. If it meets all their requirements they will put a smog referee sticker on it and you smog it like you would for the year of the motor from then on out. So if you put a 2010 Hemi in it, the referees sticker will show all the required smog equipment and year of the motor so when you do smog it, the smog tech will look at that sticker, do a visual inspection on what is supposed to be there, then either dyno or scan the computer. Once you have the sticker, smogging it is no different than smogging any other car. There is no extra cost, no special tech needed. etc. I had a 1989 Ranger and swapped in (smog legally) a 1990 5.0HO in place of the factory 2.9l V6 and it was smog was a non-issue after the ref installed his sticker.
DO NOT try to beat/trick the system! DO NOT install non-smog compliant parts or you will regret it! DO NOT Listen to anyone that says "Yeah, you can install that even though it is not smog legal, no one will ever know." If you tick off the smog people bad enough, they can black list your car and you will never get it registered in CA.
All of this is expensive. If you are doing an engine swap yourself, expect at least $3,000 unless you are doing an AMC V8. You could do an AMC 360 back in yourself for about $1500 or less if the engine does not need a rebuild. If you are paying a mechanic, get your wallet ready; it's going to hurt. I think this is a big reason babywag said
Originally Posted by babywag
... the seller was dishonest and "took care of smog".
If I was the buyer that purchased a vehicle with a recent smog cert., then found out it wasn't legal/compliant heads would roll.
In CA the seller is responsible for smog to try and limit people getting screwed with the purchase of a vehicle that isn't compliant/legal or needs hundreds/thousands in repairs to make it compliant/legal.
The law is an attempt to protect folks that are NOT mechanically inclined and do not know how to repair a vehicle themselves.