Bc6: I'm puzzled by your fist question. The locomotive you asking about *WAS* manufactured by MTL so it came equipped with ... MTL couplers! Do you have one of those models and it doesn't have MTL couplers?
To answer your question, looking at my units, the B unit uses a short T-shank coupler (MT7, like ones used in kit #1161) but it is housed in a non-standard coupler pocket which is also part of the model's lower frame. In front of the A unit the coupler looks like #2001.
As far as replacing the drawbar with couplers, that should be doable using the complete coupler assemblies which are used on the rear of the B unit as they look like they will be a direct replacement for the drawbar unit. If you contact MTL, they will most likely sell those to you as spare parts (assuming they still have any left). But why? FT A and B units in real life were pretty much permanently coupled.