I don't believe you will find another engine other than a willys L/F134 that will fit that bell housing.
You can change the bell housing to the one used in the flat head 226 and the OHC-230 wagons and trucks, replace your T90 input shaft from the shorter one to the longer one and pick up an adapter from Novak and the world of Chevy v8's and v6's opens up to you. Used Chevy Vortec v6's are available and cheap. T90 is marginal for even a mild V8, but it is often done.
Another popular swap is to go with a Dauntless V6. It was actually used for a few years by Jeep in the CJ5, so you know installation parts are available.