'Bolters helping 'Bolters is a beautiful thing!
Not all GM engines were created equal -- just because it's a GM engine, doesn't mean it will just bolt up to your GM transmission or driveline -- you need to mate correct bellhousings! Good thing Les Parker can tell you...
A little information may be helpful!
Before we get started:
If you are putting a V8 or late six in your truck, you will need a V8 angled side mount cast iron truck bellhousing from 1955 to 1968. They all fit the 168 tooth flywheel. The aluminum bellhousing will not work without major cutting on the cross member. The only difference in the cast iron ones seems to be which starter is required.
Some common side mount, V8 bellhousing casting numbers for trucks are, 3738373, 3765710, 3733365, 3815891, and 3925505. There may be others. All those numbers fit the 10 1/2" or 11" clutch and the 168 tooth flywheel.
There are three common starter bolt patterns for the V8 or late six. The earlier ones bolt to the bellhousing with three bolts. All those are for the 168 tooth flywheel. The other two types bolt up from the bottom and to the engine block. The starter with the two bolt holes 90 degrees to the crankshaft is for the 153 tooth flywheel. The starter with the bolt holes about 45 degrees to the crankshaft is for the 168 tooth flywheel.
Use whatever starter your bellhousing requires. Late starters will not work with early bellhousings due to starter nose interference.
Beginning with the first Chevy V8 in 1955, all V8 flywheels are either 14" diameter with 168 teeth, or 12 3/4" with 153 teeth. There are no other sizes. The early 168 tooth flywheels have a bolt pattern for a 10 1/2" clutch. The later 168 tooth flywheels have a bolt pattern for an 11" clutch.
The 153 tooth flywheels have a bolt pattern for the 10 1/2" clutch only.
From 1955 to 1962, the only V8 flywheel was the 168 tooth. The smaller 153 tooth flywheel was introduced in 1962 or 1963.
Almost all trucks came with the 14" 168 tooth flywheel drilled for either the 10 1/2" or the 11" clutch. There may have been a few drilled for both sizes, but no one I talked with has ever seen one.
The bolt pattern for the flywheel to crankshaft changed in 1986, but the bolt pattern for the clutch stayed the same.
In 1986, Chevy engines went from a two piece rear main seal to a one piece rear main seal. The hole in the center of the flywheel and the bolt pattern changed completely, but the clutch pattern stayed the same. This means that if you put a 1986 or later engine into your truck, it will all bolt up -- except for the flywheel. You have to use one with an 1986 or later bolt pattern. Your clutch, V8 bell housing and most transmissions will bolt up.
There has been a lot said about clutch disks here on the 'Bolt. I'll pass on that for now.
I'm sure folks will find corrections to and omissions from the above. I hope so! Note them and add them. I'm guessing that I've just scratched the surface.
We live in the land of the free, because of the brave who left home on our behalf.