The 216 bellhousing will be a direct bolt-on swap once the flywheel is removed. There are two bolts holding the bellhousing to the block that are hidden by the flywheel. Then you can use the original vertically-configured rear motor mounts instead of the angled ones on the later model bell housing. In 1954, the shape of the crossmember at the rear of the engine was changed, and the motor mounts between the bellhousing and that crossmember were angled at approximately 45 degrees. Your original 1946 bellhousing, flywheel, clutch pressure plate, and transmission will be a direct bolt-up to the 261 engine. That makes the only adaptation needed involving the front mount, on some engines. Drop me a PM and I'll share my phone number, if you like.
Jerry
