Is it worth it to replace the engine in my 1997 dodge dakota?

I have a 1997 dodge dakota 2WD, extended cab with a 5.2L engine. It currently has 263,000 miles on the body and engine. I'm beginning to leak oil on the ground when I'm stopped from a leak that is around the rear main seal. The thing still runs well with minor problems (cruise control no longer working mostly.) I'd like to replace the engine with a 5.2 L that has few miles (less than 50K) and keep it running for another 2 years. Is this possible? I know it's definitely not a great investment but I don't want car payments and can't afford to buy one outright. I think that $2K to replace the engine would be a small price to pay considering $2K wouldn't buy a new car worth having.