The 1929 - 1957 Chevrolet Master Parts & Accessories Catalog
Shows two throwout bearings.
Group # 0.79936-56 part # 909422 1 7/8" long
55-57 part # 900018 1 9/32" short
Looks like part # 900018 was only used on 261 cubic inch 6 cylinder and V8 engines.
If I were you I would first try to ID my engine, flywheel and clutch housing.
Then I would buy the correct pilot bushing for the crankshaft that is used in the engine.
In one
POST you said"
I installed a new throwout bearing and clutch.In another
POST you said"
I used the old clutch disk and the old pressure plate as they appeared to be good.
Did you use the old clutch disc?
What kind of problem were you having that made you pull the transmission?
Why did you think the pilot bushing needed to be replaced?
Because it is such big job.
When I replaced a bad clutch I always installed a new clutch disk, pressure plate, throwout bearing and resurfaced the flywheel.
I may have lucked out, but have never bothered with the pilot bushing.
Coil spring clutch illustration Diaphram spring clutch illustration 
