Personally I would only get the DX if it was a solid body, not rusted out at the jack points, or where the pan hard bar bolts to the body, rear fenders are also a pain to deal with if they are rusted out, front fenders on all of the first gen CRX's are plastic and you can get new, reproduction fenders but I don't know where, everything else about the first generation CRX's engine is pretty much only common to those 4 years of CRX's, swapping in an engine from another year is an investment in time and money that most people are not willing to undertake and for good reason.
Even with the CRX DX you should still get 40+ mpg if everything is running right and you can always start with easy simple stuff, like 14" Honda Insight, Civic Hybrid or other light weight narrow smooth 4 x 100mm wheels with low rolling resistance tires (main reason for 14", 13" LRR tires are difficult/impossible to find) and then swap other parts as you have the time and money, you could even skip the HF engine block and just swap head, intake and carb, main reason for the HF block is different pistons/rings, then the transmission swap is pretty cheap and easy.
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