Hunnicut has excellent books on the Pershing and the Patton that, together, include the M26 and the M46.

Some differences you can see (others were the engine, fire control, etc):

Added track tension idlers (Small rollers in the rear)
Raised the sprocket
Redid the rear deck
Fender-mounted mufflers
Redid the rear plate

Things shared with the M26A1:
Modified turret to remove the wheel brackets on the starboard side
Muzzle brake reduced to a single baffle
Bore evacuator added

Two notes:
1) The M45 is essentially a Pershing with a 105-mm howitzer rather than the 90-mm main gun. Everything else appears the same from the outside.
2) Some M46s were built from the ground up at the factory as an M46. Others were M26s that were converted in the maintenance depots.