need help

In your case, you have the GM 2.5 "Iron Duke" engine so a 304 will not bolt in without a bellhousing change too. A GM 2.8 or 3.1 V6 will bolt right in and give you a lot more top end power and a bit more low end too and not overpower current driveline.. A GM 231 V6 from a buick should bolt in too. GM sold 225 V6 and all right to it to Jeep before AMC bought them and then AMC sold the engine back to GM in late 70's and GM tweaked its original design and increased it from a 225 to a 231 and put it in cars and still uses the block to this day. Also the old 2.8-173 and 231 V6 will respond well to build ups and with proper gearing will deliver some good performance and weight a few hundred pounds less than a 350 and get better MPG too plus have less cooling issues. It would run well with even a stock 231 in it compared to what you have now and it would still be a "Jeep" because though GM owns 231 engine rights now, Jeep did for several years when it was a 225 so they used that block before.