Quickest way to determine if you have a 1955 265 engine is to look for the engine stamping on th RH side of the block just forward of the head. The last 4 or 5 digits and letters will give you the plant of engine assembly, year('55). and transmission type. if the stamping is 55 then you should have a 265 (unless someone has faked it). exmpl. 0001001F55F would be: plant Flint, year 1955,transmission powerglide. The casting # for a 1955 block is 3703524. You'll find this on the rear of the eng. drivers side just below the head. Sometimes tough to see with engine installed. I am running 205/75R-15 wide whites on my '56; no problem.