This is a MRP 550 stock motor introduced around 1980, based on an Igarashi teardown. As all other ROAR certified motors of this time frame, this means a 35 Turn/ 23 AWG winding.
The MRP550 motor was very popular in it’s day. We have seen several photos of A-Main cars using such motor, even on International level.
Based on the 550, there were also other MRP motors with different levels of reworking. Zapped magnets, dynotested, rewound and balanced armature, soldered windings, cutted commutator, etc. Depending on level, these motors were sold as 551, 552 or 553.
553 was the full blown modified version.