There is a drain plug on the pan and there are several in the torque converter. Just turn the engine SAFELY until one of the torque converter drain plugs is at the bottom. Drain the pan and the torque converter and refill. Make SURE that you get the correct reading on the stick under the CORRECT temperature conditions.

Especially in your climate, there is no need for synthetic ATF IMHO. The 5W 40 might be a good choice for your climate. The M103 has sliding cam followers as opposed to flat tappet, so it might not be necessary to run the Fleet type oil in the engine. I like the added detergents for keeping it clean, and with a flat tappet engine the zinc additive to some level is necessary, but in your situation I would think that a good 5W30 would get the job done.

My $0.02,