Personally I have put 4 accu-triggers on non-accu-trigger actions. No milling required for any of those installs. The actions ranged in age from the mid-1970's era to current production, all with side mounted bolt release.

All I did to install was to clip the tip off of the rear accu-trigger spring, meaning the little tip that fits into the hole on accu-trigger actions (see blue arrow in pic). Then I melt out the thread locker (lower red arrow) on the adjustment screw (upper red arrow), so I can adjust for the proper engagement to the safety bar, and install like normal into the action. All 4 work great, just like they did on accu-trigger built actions, and all adjustments are the same otherwise, and of course I removed the wire spring and little adjustment screw that was used on the old style trigger.