Chevy Clutch Housings
Most people define Chevrolet Bellhousings by the Clutch size (i.e. 10.5",11", or 12"). Flywheel Diameter (12.75" or 14") or number of teeth is more accurate because some 168 tooth flywheels are drilled with multiple bolt patterns, and the aftermarket makes a 153 tooth flywheel that a 11" clutch and pressure plate will fit.
Chevrolet has always had just two sizes of flywheel: Big (168 tooth 14" diameter) and Small (153 tooth 12.75" diameter), with the 153 tooth flywheel being introduced in 1963.
The early bells were cast iron with the aluminum bells being phased in. Eventually aluminum became the only material for all factory bells.
With that said, most Chevy bells will physically fit Small Blocks from 1955 on up, 6 cylinders from 1963 on, and all Big Block engines, W engines, as long as they are Chevrolet engines. GM used engines from other divisions in Chevy cars.
But, there are major differences to consider such as transmission mounting hole size, clutch fork ball stud locations, z-bar mounting provisions, starter, clutch fork hole location and, of course, factory correct application.
In the above photo you can see the difference between the starter sides of the two aluminum housings. On the 168 tooth bell, the starter is farther away from the crank center line and therefore needs more room in the bell.
Paint: Most Chevy bellhousings I've come across were panted while attached to the engine and transmission, and have over-spray in various places on the inside (starter hole, fork hole) with the outline of trans mounting ears on the front. This isn't heavy, just over spray.
Inspection covers: I've found three different sizes for aluminum bells. 153 tooth, 168 tooth and truck. But, there are variations in the starter hole.
Date codes: Most cast iron bells have an alpha numeric code. Aluminum bells? I saw discussion on a forum that the single number over the part # was a date code, which I doubt. Manufacturers usually put a number in molds and dies to help with quality control(as in number seven cavity needs maintenance).There are one or two circles divided in half that are Engineering codes and may contain some sort of date code. I have seen a few bellhousings with 80 in the circle; these are obviously date codes. Some bells have a graph-looking thing with dotes also. I will try to research these.
For pictures,applications and more details click on the Picture or part number link.