Will 8-3/4 alxes fit in the old 65 7-1/4 rear?

leblanc said
8 1/4 might be your cheapest and easiest way out depending on your HP output. These rears are usually good for about 400HP.
(just another option)

I'm in S.E. NC and need a BBP 8 1/4 rear axle for my 65 Dart. Are these only in the 73 to 76 years? Every bone yard I call says they don't have anything this old :(.