If you want a tough convertor that will hold whatever you put in front of it give Torco in Abilene, TX a call. From what I am told they bought Art Carr a while back and now build their convertors with the same stuff as Art Carr uses. I bought one of their convertors for my S-10 and it is the nicest one I have owned. It is 100% better quality than the TCI's from an external standpoint. They actually use a one piece billet rear plate that is the back of the convertor, hub, and mounting tabs all in one. I told them that the convertor would see 800lb/ft of torque and the just said "no problem". My 10" convertor was $325 shipped to my door step and comes with a guarantee to stall to the designed speed or they will restall it. They will also rebuild the convertor at any time for $100 regardless of condition.
Of course, when you order the convertor they are going to want to know everything about your car. If I were you, I would have it built for the big engine. If you get it stalled for the small engine, it will stall alot higher with the big engine. Stall speed is simply a result of the amount of torque that is applied.....that simple.