Idea is great. But the gearing, when drill is placed to the motor axle..

Drops the rpm of the drill to 1/4 -1/3 of the drill speed.
So blade runs about 500rpm. I think it would be possible better if the angle grinder head would be used in the way that it increases saw blade speed, drills usually have enough torque allready. Then you could get 500rpm cordless drill to spin saw blade with more suitable 2000rpm. Just my toughts.

Idea is great and its easier to make this way, thumps up from that.