I am copying this information over from the old 63/64 site. In time I will continue to add to and edit as needed.
1963 390 and 1964 429 Engine History and Differences
-The 1963 390 was a totally redesigned engine compared to the 62 and earlier 390's. It was 50+ lbs lighter, engine accessories including the distributor was moved to the front and used a new aluminum engine cover that incorporated the oil pump, the length and height were both shortened, they switched to a hollow-cast crank and switched to an alternator-rectifier charging system. The bore, stroke and horsepower (325) were the same as the 62 390 however this was a lighter, more agile 390 than the old design.
- For 1964 they took the new redesigned 63 390 and increased the bore and stroke increasing the displacement to 429 cubic inches and horsepower to 340.
-They also used two different crankshafts on 64 429's (see Transmission section below)
- The 1964 429 used with Hydramatics had a crank with a raised rear "drive plate" mounting area that was 3 3/16" across.
- The 1964 429 used with Turbo Hydramatics had a crank with a raise rear "flexplate" mounting area that was 3" across.
-Other than a few other minor changes including redesigned right exhaust manifolds, larger higher capacity oil pump gears in the front aluminum engine cover, air breather housing inlet enlarged, power steering pump cooler added, etc.) the 1963 390 is very similar to the 1964 429....especially the 1964 429 with the Hydramatic crank...as they will both mount up to the older style Hydramatics.
-In 1965, the engine was moved forward, the motor mounts were changed, the oil pan was changed to a front sump pan and their were other changes such as pistons that are different from 1964.
Hydra-Matic and Turbo Hydra-Matic Transmissions
- In 1963 all body styles came with the Hydramatic (shift pattern PND1D2LR and sometimes called Jetaways) transmission and bolted directly to the back of the 1963 390 block.
- The Hydramatic transmission between 1961 to 1964 will interchange with no modifications. They changed the reverse cone in 1962, but the transmission housing itself is the same.
- The 75 series and Commercial Chassis Hydramatic were slightly different in that they had a heavy duty reverse clutch and higher capacity oil pump, however, they are externally physically the same and will bolt right into a regular body style. (I put one in a 1964 62 series coupe some time back.)
- In 1964 the 62 series, 75 series (limos) and commercial Chassis continued to use the Hydramatic and again bolted directly up to the back of the 1964 429 block.
In 1964 the DeVilles, Eldorado and Fleetwood 60 Special Body style went to the "Buick Borrowed" and new for 1964 Turbo Hydramatic (shift pattern PRNDL and sometimes called Turbo 400 since other makes have called it by this name over the years. In order to bolt the "Buick" Turbo Hydramatic (sometimes called Turbo 400) to the back of the Cadillac 429 an adaptor ring was used.
- The 1964 "Buick Borrowed" Turbo Hydramatic was a one year transmission as the Bell Housing was changed in 1965 to allow the transmission to mount directly up to the 65 429. There were also some other internal changes and the new 1965 THM had a 2 Drive Range as seen in the shift quadrant picture below.
- Swapping the Transmissions
==> While the hydramatic drive plate with the 3 3/16" center opening will mount right up to Turbo Hydarmatic crank since the bolt patterns are the same, there is a gap and will usually rip out in short order.
==> the Turbo Hydramatic flex plate opening has to be opened up to exactly 3 3/16" to mount to the Hydramatic crank end and...if it is not exactly centered and a snug fit it to will quickly rip out.
===> A best option is the swap out the correct 429 crank designed to find the Hydramatic drive plate or Turbo Hydramatic flexplate.
Other Difference between Hydramatic and Turbo Hydramatic equipped cars
To go from Hydramatic to Turbo Hydramatic or vice versa consider these additional difference between cars with the Hydramatic and the Turbo Hydramitic
==> Front driveshaft section on TH equipped cars is longer (putting a TH in a 63 or 64 limos requires the front drive shaft section from a 1965 limo)
==> Front cross member Yaw Mounts and the rear transmission mount are different
==> Starters were different
==> 1964 Turbo Hydramatic has adaptor ring, hydramatic doesn't
==> TH uses electric kick-down switch, Hydramatic used the TV Rod
==> Instrument cluster shift indicator display (PRNDL on TH and PND1D2LR on Hydramatic.
==> Hydramatic uses a drive plate that mounts to the torus while Turbo Hydramatic has flexplate with starter gear teeth that mounts to the torque converter
==> turbo Hydrmatic had vacuum line from vacuum modulator up to vacuum fitting on back of carb where brake power booster connects
==> Neutral Safety switch is different if swap out is in a 64, due to different in shift pattern