From personal experience Mato 3:1's are not a drop in for the KV-1. For each gearbox there are three bosses in the HL hull for mounting. Only one of the existing bosses is useable for the KV-1 (same for the PZ III which I also installed Mato gearboxes in). I had to install my own bosses using epoxy and computer standoff nuts. Asiatams gearboxes only require the install of one standoff on each side. Also the alignment of the Mato gearboxes are poor. I had to open the mounting holes up to get the output shafts to be perpendicular to the hull. The last thing is the assembly is shoddy. A number of the brass stops that are held on the gearbox shafts with a set screw were loose. One of mine came loose, jammed the gearbox, bending the gear/shaft and burning out the motor. I had to tighten all setscrews and install a new motor.
This is all relative to the Asiatam gearboxes I have installed in my Stug III which have been flawless. Needless to stay I will be spending the extra $10 for Asiatam gearboxes in the future. The only added item to deal with on Asiatam GB's is the out put shafts are larger than stock or the ToMatos, which requires you to ream out the drive sprockets to the larger diameter.