The biggest problem, isn't just that you're adding weight, it's where you're adding weight.
Again, this all depends on what the OP really wants to do with his Jeep.
I street drive, sand drag, and run the sand dunes with mine. When I ran a 427 ci SBC, I was able to put down faster times than another Jeep with a 496 BBC. His Jeep actually weighs less overall than mine does (though not by much). But, he had an iron headed BBC over the front axle, putting a huge weight ratio in the front. That weight distribution problem caused traction problems. Even with more tire, he was a couple tenths slower than my times (and we're talking an easy 100HP difference in motors, his making more).
So it's not just about the overall weight.
434 pump gas SBC with an NX/HVH plate system
th350/Coan 5,000 converter/Dana 300 tcase
Dana 30 front with 4.56's/Dana 44 rear with 4.88's