This RIF is a bit of a mystery, from what I can tell it started out as an MC51, and was then fitted with an SG1 stock, and a rifle length barrel extension after the handguard.
The most interesting part is the receiver, Tokyo Maruis are plastic as standard, this is a metal one, brand unknown, very nice fit and very sturdy.
Original TM gearbox was cracked at the front, replaced with an aftermarket shell with larger bushes. Radiused to prevent future cracking. 
16:1 gears. 
High torque motor. 
Original TM hop unit, with Modify? rubber. 

Shoots very well, nice and snappy on a 7.4v, video available on request. 

Includes 9 total 70rnd midcap magazines. 

Two small issues, very slight wobble from handguard, and grip baseplate screws replaced with incorrect type at some point, still secure. 

Postage £15 with payment by PayPal or cash on collection. 

Please text or message with any questions/reasonable offers.