A833 early gearset in OD case?

On all that being said, I can understand the stock OD case being weaker than the iron case.
Will it be weak or just weaker. Would it be as strong as a cheby ST10?
with the countershaft float issues corrected of course.
was thinking about this for a street small block in a 63 dart.
probably 400Hp with 3:91 ratio.
Thank you for your input