Earlier RIAs and Armscorp had problems with grips and grip screws.
Charles Daly (Another from the PI) would not accept a Colt slide release.
The differences are small, but increase the work needed.
Get a copy of Kuhnhausen's books, grab your micrometer, and measure.
This is based on my experience, not conjecture.
"A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed."
Life Member NRA
Life Member NAHC
Former President of the ECPT (Eifel Combat Pistol Team)