I have never done it but it shouldn't be too hard to do. I would assume that your frame is very similar to a Tempest/GTO of those years so if you used the frame mounts, motor mounts etc. from the same year as your truck it should fit with out too much trouble. Unless you have a dual bolt pattern on the trans you would have to change to a POB type trans. I swapped a Pontiac 455 into a 1961 Chevy PU using a combination of Pontiac and 1976 Chevy truck parts with no cutting or welding necessary. Good luck if you try it.
I'm hoping to use the long tail TH-400 that's with the motor now... Cliff Riggles the Quadrajet guy built them both and they run well...
I always wanted an El Camino but didn't want to get away from Pontiacs, I think this is the best way to go... The car in the photo is just from the internet, I'm still looking for a 68 to 72 El Camino preferably a roller..
Long trans might give you some problems but I'm sure you can work around it. If you used a later El Camino you could use mounts from a late 1970's - early 1980's GP with the 301 engine. I saw one at a car show where the owner made it into a Grand National PU with the Buick Regal nose on it and the turbo engine. Very neat. Again good luck.
pontiac into 72 is not easy. All accessories have to be swapped left to right and vis versa. Battery on wrong size. only short T400 trans will work. frame mounts bolt differently.
Thanks helper. The car I bought is a 69 SS396. It came with a very low mileage 1978 427. I'm keeping this set up. This 427 has torque and runs nicely. I never owned a 427 I didn't know how nice they were.. I think the engine came from a demolished dump truck with very low mileage.. Then it sat for decades until the owner picked up this el camino that was part of a truck load of old cars that he bought, he's a very wealthy man..
The el Camino is a dream to drive. The massive frame they put under these cars makes them handle like a expensive high performance go cart... I bought it for 12 and had to put a new interior in it and added the Hurst Autostick I. That shifter is a dream to drive.. John De Lorain wanted every 69-72 Grand Prix to have one of those shifters..