I have a 63 catalina wagon first Pontiac i love this car but my trans has died on me... this is my daily car and need some dependability out of her I am wanting to swap my 389/ slim jim with a 350 outta 75 Le Mans  so my question is this


how different are these blocks? as far as mounting, length, etc. Will i need to make new radiator support, mount locations and can i use the AC (never owned a car with one of those before)and the drive shaft?

What sorta problems will i need to watch out for?

I'm hoping to pull around a small camper this summer  allready got a heavier suspension on the rear with air shocks.  would the rear out of the later car serve better for this?

Thanks alot for any help anyone can give i am very excited about this project.  

Hi lonli1.
Al pontiac v8 engine blocks except the 301 and the smaller one(don´t remember the correct size but I think it´s 265 cui) are about the same. The difference is the starter and probably the engine mounts. On the 75 engine, the backside of the starter is mounted towards the front of the car. On your vehicle I guess you have the starter mounted the other way if it´s the original engine. This might be a problem if you gonna use your original transmission. You can´t mount a start when the original 1963, 389 starter goes into the transmission.
On the 75 350 you will have several choises to place the engine mounts so this will not be a problem. My tip for you is to use the pontiac 350 engine with a th-400 transmission. That is the combination that I use myself.
Good luck!  

You don't necessarily have to ditch your 389, there are adapters available (try Trans Dapt or Ames maybe) that will allow you to bolt-in a th350 or th400, with the starter now mounted to the adapter plate instead of the trans. Then you only have to worry about the shift linkage, rear crossmember mount and drive shaft. If you choose to swap the engine and trans there are adapter kits for the late block into early chassis for the motor mounts as well. Don't know about your accessories though, I assume you mean the 63 Cat has A/C and you want to keep it not try to install the 75 Lemans A/C. Way easier to use a Vintage Air kit than adapt the later model stuff.