oldblu49, I bought mine from Master Power Brakes.
It looks identical to Alvins but was considerably more expensive. headscratch
AFAIK it can also be used with a manual trans,but I cut the clutch arm off and used the remaing part as a spacer.I'm running a TH350C.
It uses a smaller 7" diameter booster so clearance is a little better,but it is a true bolt-in.
Here's a pic of mine installed.

1950 Chevy Advance Design 3100 in Scotland
In the Stovebolt Gallery
More pix on Flickr.
I've definately got this truck thing in my blood ... my DNA sequence has torque settings
"Of all the small nations of this earth,perhaps only the ancient Greeks surpass the Scots in their contribution to mankind" Winston Churchill.