An amc v-8 would be easyest. It would bolt to he trany but that dont mean it would last. I'm not real familiar with the trany's used in wranglers so i cant help you there much. Alot ofit depends on how much work you are capable of and willing to do. You might consider building the 6 cyl. I have seen poeple get 350 horses out of them and thats almost double what a stock 304 puts out.
Al
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Al
My web page