Engine swaps can be accomplished without too much aggravation if the vehicle and donor are similar. 1980-90s Jag XJs are swapped all the time. Monster Miata and small block Z-cars are other examples. The key to a swap that will make it past the referee is that the year of the car and the year of the engine be the same. It is usually very easy to retain the donor engine related emission equipment, fit the OEM cat, etc., but when the engine is newer than the vehicle the evaporative system is not certified for the newer year engine. No matter what you do to try and update it, the only way it'll fly is to install the entire system from the donor car which is usually not practical/possible. For a '79 X you can swap in any '79 engine you like, but what would that be exactly? Another misconception is that '67-'75 smog exempt vehicle have a free ride. The reality is that while the bi-annual test is waived, it's still illegal to perform a swap or tamper/remove any of the original emissions equipment. Is it a big risk to take? Not really. Although the ARB does set-up roadside sniffers with photographic plate recorders once in a while and roadside checkpoints, it's rare, but it does happen. Only safe avenues in this state to be free of requirements are to build a replica (Cobra, GT-40, Lotus 7, etc) and register it under the SB100 program as a 1966 or below. The only emission requirement is a PCV. Or, don't fool with anything other than pre-smog cars ('66 and down). Those you can drop a radial Lycoming in them if you want because no smog laws existed at the time of manufacture. There are no retro smog laws in the state except one. All vehicles must have a closed crankcase ventilation system regardless of year. Anything with a road draft tube, even a Model T has to be modified to a closed system. For anyone trying to use logic in thinking their K20 swap is a 100 times cleaner that what the car originally had, don't waste the effort. In a state with cities that outlaw charcoal for BBQ grills, we're just lucky these bureaucrats haven't outlawed driving any car over 10 years old - at least not yet, but give it time.......... One final note, if you play around the edge of the law in California (modified 67-75 car, claimed a low value for sales tax, have out of state registration and plates on anything, etc.) stay far away from Cars and Coffee and local show events. ARB and DMV investigators have been known to be in attendance now and then, and it's not because they are car enthusiasts.