The engine is the original one it came with but I had it rebuilt (rings were worn) and that increased the bore (now 40 over) which required new pistons. That changed the compression (we chose 10.5:1). I have the original Motorcraft carb but 10 yrs. after rebuild, the motor would shut off while driving. This happened several times and I had several mechanics check all the systems - narrowed down to carburetor. Carb was taken apart and new kit put in but same problem so that is why I sprung for another carb and it is working fine. I need to get the original rebuilt but I'm trying to zero in on what exactly is wrong with it. I'm leaning towards ethanol. I was using Petro Can 74 octane gas in the car and that has ethanol.