started my 1965 Barracuda today....
There's a really quick & easy way to tell without even taking a wheel off. Look at the attachment point of the knuckle (spindle) to the upper ball joint. If it's perpendicular to the drum, you have 10". Parallel to the drum & you have 9". The 9" also looks quite a bit wimpier. Here's a 10" drum spindle (using Wilwood disc).
There's a really quick & easy way to tell without even taking a wheel off. Look at the attachment point of the knuckle (spindle) to the upper ball joint. If it's perpendicular to the drum, you have 10". Parallel to the drum & you have 9". The 9" also looks quite a bit wimpier. Here's a 10" drum spindle (using Wilwood disc).