From what I could gather from the site link below
The 1963 326 has a different type crank hub to accept the Tempest Torque rear transaxle drive line coupler.
Measure the pilot recess on your 63 326 crankshaft .In order for it to accept a Pontiac/GM dimensioned pilot bearing it or convertor hub . Look at the dimensions below & compare to what you measured.
The Pontiac uses a rolling element-type pilot bearing as opposed to a bushing.
BCA p/n 7109 pilot bearing
Pilot bearing is BCA p/n 7109 (available from Summit). The GM part number is 15533265. The dimensions are 1.3780" OD x 0.5906" ID x 0.3543" wide (35 mm OD x 15 mm ID x 9 mm wide). According to www.pontiacpower.org
, the cheaper p/n 6202 bearing may be used, but the crank opening may need to be machined 2 mm deeper. The p/n 6202 is 35 mm OD x 15 mm ID x 11 mm wide. The 6202 is available with shields on both sides to keep dirt out.
The outside of the crank opening is staked with a chisel in at least two places to hold the bearing in place (Or loc-tite can be sparingly used) because the pilot bearing is a slip fit into crank recess.
Then there is this problem:
Also watch the pilot ID on early pre-1964 389 & 326 Armasteel cranks when using an automatic
The flexplate has to match the flange diameter for the 326 so careful ckecking before purchase of the flexplate is a must.
Modern GM transmission behind early Pontiac engine:
Due to the differences in the early crank flange and the lack of a drilled block mounted starter mount on the block, a TH 350/400, etc. tranny won't work behind an early (pre ~1964) engine. Wilcap and Bendtsen's sell kits that allows the later trannies to bolt up behind these early engines.
So can it be done?
Yes very carefully. Some minor machinie work to the crank pilot may be required.
It will be a custom installation.