I have replaced rod bearings, main bearings and piston rings with the engine in the car on my 1941 Dodge Coupe. If no damage to the crank, which can't be known till you get in there, and the oil pan can come off with the engine in the truck, then yes it can be done in truck. If it is a temporary repair to get by until the "good engine" can be swapped in, I would go for it, rather than have it undriveable as is. That's just me and how I do things, not for everyone. I would rather drive a good car than own a great car.