I'm going to bet that your 235 uses a single front mount with two bolts. thats how mine is. The 350 that's going into mine has side mounts, so I'm planning on firing up the welder and making my own custom mounts. I have seen, however, conversion mounts to adapt a 350 into just about anything. Might check out
Summit Racing for something like this
Motor mounts . Somebody else might also have some ideas on where to get mounts.
Also, plan on finding a different bellhousing. One from most V-8s should work. I found one on ebay for $20.
Gas milage? I've come to accept the fact that these trucks are so stinking heavy, gas milage is just going to be bad. I'm doing good if i can get 9. 8 isn't too bad. I've seen down to 7 before.
You have any pics of your truck? Is it 1/2 ton or 3/4 ton?