from Don at AACA
First answer No, not exactly a 63 326 Pontiac is really a 336. It's dimensions are bore 3.78 X stroke 3.75. In 1964 the 326 really becomes a 326 now at 3.72 X 3.75 and doesn't change till the end of it's production life in 1967.
The 4 cylinder ( 1/2 of the 389 V-8 ) engine and the 63 326 have many different parts. Differences in the engine mounts, torque tube/shaft and trans between the 4 and 8 cyl Tempests are different. So even a 63 326 V-8 couldn't just be swapped in. There are also differences in the 63 326 and the 67 326 externally. There are differences in the starter mounts, crankshaft ends, etc. between early (1963) and late (64-67) 326's.
As far as the transmissions go you are really looking at apples and oranges. 1961-1963 Tempest use a transaxle ( clutch, or converter if it's a automatic, transmission & third member and axle combined in one unit) and it's located in the rear of the car and has a flexible rope drive shaft in a torque tube that connects to the engine in the front of the car.
The automatic transmission from the 67 326 is not a powerglide. It's a ST300 and it's a four range two speed automatic that is bolted to the back of the engine in a conventional driveline manner.
Hate to be the bad messenger here, but that's how it is.