This is the most common Grizzly pistol related question that I hear. When I asked the inventor of the Grizzly handgun (Mr. Perry Arnett) this was his reply to me...
Let me see if I can recite them accurately:
The only Grizzly Pistol parts that DO NOT interchange with a standard 1911-A1 are:
Slide
Receiver
Trigger bow - longer
Firing pin - longer, smaller tip diameter
Firing pin spring - slightly stronger
Extractor - longer
Barrel
Recoil spring - 26# and longer
Barrel bushing - must be of the 'short' [Commander] length
All other [49?] parts from a standard 1911-A1 SHOULD interchange with a Grizzly Mark I (or II).
Any of the old brochures that were shipped with the Grizzly pistols will have a similar list.
Perry
To learn more about the "REAL" history of the Grizzly pistol and Perry's design click here:
Arnett Patent Grizzly Technology History