Hy berts53, if you are working with a 1953 truck, the bellhousing to frame mounts sit flat on the crossmember, the 54 and newer crosssmembers/bellhousings have an angled mount. So the two different bellhousings only fit their complimentary design of crossmember. So in short if you're trying to install a 1958 engine in a 1953 chassis, then you must use the bellhousing for the 1953 chassis, hope that helps.
