cast iron 833

So Ive come across a very early A833. It's from a Dart or other A,and is a cast iron body/bellhousing. This is the number off the side,C 95639 U. The only catch is it's a ball and trunnion flange,and is missing the reverse rod.Now I know this trans will take whatever I throw at it.Comes with trans, bellhousing, shift gate, some linkage, clutch fork, boot and throwout bearing for $200.

My original plan was for a 727,but then I realised there is no o.d gear except for xpensive GV,so started looking at overdrive 833's as a reasonably priced option. The o.d would hold up to the 400 that I will start out with,allowing me to use a 3:91 gear out back without the highway rpm penalty.

Eventually I'll replace the 400 with a 451 that will most definitely kill the A-833 overdrive.Unless theres a way to built it so it will live,I'd need a real 833.

Thats where this cast iron trans comes in. I could also use it behind the 400 and simply use highway gears,most likely 2:94 or 3:23.

So whats my question? Which trans is the better choice? The cast iron beast,or the alum case o.d?