Blown head gasket additive?

I'm considering a adding a stop leak additive, until I can get it into the shop for repairs. I'm planning on replacing heads and gaskets.

1. Do you guys know if I could harm anything else by adding stop leak?

2.. Also... I'm having trouble locating the coolant drain plug on the block of the engine? Anyone know where it's located?.

3. If I do choose to add a stop leak, can anyone recommend a Pacific brand?

It's a 26 hp Kholer Agis liquid cooled engine. PROCHEM peak gtx.