Motorshield H-bridges isolated between outputs?

[Schmigneous]

I'm planning to power two micro metal gearmotors (http://www.pololu.com/catalog/product/1101) using my Arduino Motor Shield and a 7.4V li-ion battery providing independent power. I will need to beef up the H-bridges to handle the 1.6 A stall current for each motor.

My question is this: if I connect the motors to M1 and M2 on the shield, can I just upgrade the one L293D or do I have to do both? It appears from the shield schematic that they are wired separately (i.e. IC1 controls M1 and M2, IC2 controls M3 and M4).

Also, I planned on piggybacking two SN754410 chips plus a heatsink. Is that overkill for this setup?

[adafruit_support_bill]

if I connect the motors to M1 and M2 on the shield, can I just upgrade the one L293D

Yes. The L293D's are independent of one another.

Also, I planned on piggybacking two SN754410 chips plus a heatsink. Is that overkill for this setup?

I wouldn't call that overkill for motors with a 1.6A stall current. It is always good to have a bit of a safety factor. The cooler you can keep the chips, the longer they will last.