360 converter

Well, today I went to have a closer look to the very first car I had as a 19 year old. You can have a look in the following thread
http://www.forabodiesonly.com/mopar/showthread.php?t=42251

Anyway, it now sports a 360 engine (with the original 904 tranny) instead of the 273.
And the seller told me it needs to swap the converter from the stock converter, because of severe vibrations
He has bought a used converter for a 360 that will follow the car in the sale.

Now I wonder if any converter from a 360 will work or does it have to be balanced together with the specific engine?

He will also let a 8 1/4 rear axle follow the deal. How far can I strees a 8 1/4.
Any thoughts are greatly appreciated.
Thanks guys