The M420 Locomotive features:
- 3D scanned from an actual M420. This is as close to real as it gets!
- MR-20b and MR-20c classes available in the first run
- Rapido’s innovative dead straight metal side handrails with plastic stanchions
- Incredible underframe detail including traction motor cables and other piping, rerailer and a silly number of separately applied parts
- Two or three panel radiators, louvered or large opening electrical cabinet door, open or closed truck bearings
- Separate grab irons and handrails installed at the factory
- Operating headlights, rear lights, tri-colour class lights, and illuminated cab control stand
- Highly detailed cab interior with optional open front door
- DC/Silent (21-pin DCC Ready) or DC/DCC/ESU LokSound

And some new features!
- CN 3500s feature rebuilt long hood with knuckle buster door latches, paper air filters, retention tank, ditch lights and relocated horn
- BC Rail has correct fuel tank size and location, four rock lights (in nose and pilot) and rebuilt steps
- B-units are part of A/B set, single A units can be purchased separately.
- P&W version has correct Type B trucks and headlight variation


The M420 was equipped with the ALCO 12V-251c3 prime mover producing 2000 H.P. Most M420 units rode on MLW ZWT (Zero Weight- Transfer) trucks. The only exception to this were the 5 units built for the Providence & Worcester, which rode on ALCO trade-in FA trucks. The P&W required a different bolster design and a slightly different truck spacing, making them unique.

MLW constructed 103 M420s between May 1973 and February 1977 for four railways including CN (80), BCR (16 including eight B units), Ferrocarriles del Estado (2), Providence & Worcester (5).

CN would take delivery of the M420s in 3 groups: MR-20a class 2500-2529 (delivered 1973), MR-20b class 2530- 2559 (delivered 1974), and MR-20c class 2560-2579 (delivered 1976). All of the CN units were retired by 1998 and today many of these locomotives have found second careers on short lines all over North America.