It's possible you have a truck housing. Mine has 3 1/4 in dia tubes. Also a strange "stick out". I don't remember the numbers but they did not match anything in the catalogs. I also have the stock roller bearings. While a PIA they do last longer than the ball bearings.....The seals leak bad so use lots of silicone. Several cruise buddies have the ball bearings and have continuous problems with them especially with deep offset wheels.
I used a Speedway weld on bracket kit and those goofy Seville E-brake calipers.
If you wind up using these you must use a 10 psi residual valve. This is noted in a GM TSB somewhere. This is the only disc brake that needs this. It helps control the piston retraction and thus the pedal travel.