What were you wondering?

Both transmissions have a good reputation, they were both used for long periods of time in lots of trucks carrying heavy loads, etc. The sm465 is capable of handling more torque than the 420.

The sm465 has a larger input bearing retainer than the sm420, so it will not fit into your stock bellhousing unless it is machined out.

The sm465 may not fit your truck (the 49) because it is so much physically bigger than the sm420.