I agree the 261 is a better engine I have ran 235's in my 46 and had to move the radiator forward to clear the water pump shaft. I put a 261 back in and was able to move the radiator back to the original spot. the original moter in the 46 was a 216, then you get all the other problems, the splasher ( not oil pump) the bearings. The 261 is a heaftier moter and you get a few more horses (about 8) with full flow oil. If it turns out that you can get a short block for the 261 and have the heads re-done, I'ld go that route.
