This kit will physically fit that firearm. The buffer spring and buffer weight are not suited for that platform though. Excessive wear may result in use with that firearm.
The Maxim Defense Industries CCS Brace Gen 6 for AR - 15 will not work on the Aero Precision EPC 9 Buffer Tube. However, you could use a standard carbine length buffer assembly with the Maxim Defense Industries CCS Brace Gen 6 for AR - 15 on an EPC9.
Yes, since this brace is built for the standard AR-15 mil-spec buffer tube system, it should fit a PSA AR-15 pistol in 300 Blackout as long as that pistol uses a standard mil-spec buffer tube.
Yes, the Maxim Defense Industries CCS Brace Gen 6 for AR - 15 will work for a CMMG MK47. The Maxim Defense Industries CCS Brace Gen 6 will replace the current buffer assembly on that rifle.
The Maxim Defense Industries CCS Brace Gen 6 for AR - 15 should work fine with that AR15.
This Maxim Defense Industries CCS Brace Gen 6 will work with a Spikes Tactical Lower Receiver. There shouldn't be a need for any modification for your build unless you use an upper that requires a specific buffer system or isn't compatible with the Maxim Defense Industries CCS Brace Gen 6 for some reason. But that would be information you would determine based on the specific upper you use.
You will need to use the buffer assembly that comes with the Maxim Defense Industries CCS Brace Gen 6 for AR - 15.
The Maxim Defense Industries CCS Brace Gen 6 for AR - 15 comes with a buffer tube.
Yes, the Maxim Defense Industries CCS Brace Gen 6 will work with the PWS Buffer Tube.
No you will not need a new castle nut or endplate with the Maxim Defense Industries CCS Brace Gen 6.