Titanium - with Funny car pedal , blow back tabs , Quad bolts (4 - 3/4" cornerbolts), and magnesium spacer to move release bearing slightly further into transmission area,  studs for lenco bolt pattern
Material : 
- Aluminum (yes there is still some out there)(* no longer certifiable ) 
- Steel Thin (* no longer certifiable ) 
- Steel with aluminum inspection cover (* no longer certifiable ) 

- Aluminum "new style" 
- Steel with steel cover and clearance hole cover 
- Titanium with all titanium components including bolts

Steel - 8 5/8 with FC pedal - covers are not aluminum

- stock - this is lakewood style stock , usually curved on top to fit door cars 
- less than 8" really old - but still out there 
- 81/8 " - these may be re certifiable for multi disc clutches - usually 2 disk 
- 8 5/8 " - most common today 3 disk alcohol some 4 disk fuel 
- 8 5/8"-converted to 9.4" 
- 9.4 " Fuel multi disk

Stock style Note: shown is with removable 
bottom and is no longer approved


8  5/8" converted to 9.4" 
 Note: spacer plate between engine and  front of bell housing,  and spacer with large internal hole so release bearing actually sits in front pocket of cannon to achieve enough clearance for 4-5 disk multi-stage clutch
Note: (right) cross shaft has also been moved further away from center  - to clear moving clutch parts and provide better geometry for fork and release bearing wide clutch fork to allow bearing to sit between arms - for additional clearance

Input Shaft, Release Bearings 
input shaft

Release Bearings

There is several inside diameters , outside diameters, depths, and an infinite list of custom lengths of the sliders to allow for the multitude of clutch sizes and input shafts sizes to the reverser or transmissions