I have rear discs on my 59 Elky-----not impressed with them at all.
Will never put discs on the rear of another car for my driving habits.
my 66 Elky with 72 front discs stop waaaay better than the 59.
There are big rear drum brake options available from the Chebby vendors.
Rear discs would only be needed on your car if you were to be auto-crossing or
race track stuff.
For driving about town and probably the occaisional drag strip run---rear discs are not necessary.