Bolting the pump to the block and use the original drive makes things easier to mount and safe some space, good engineering.

I looked at the web site and searched for what gear type this pump uses.
I had a Weaver brothers 3-stage pump on my engine and it gave very little vacuum.
I have bought a used AutoVerdi 6-stage Nascar pump with teflon coated roots style gears and when you turn the pump by hand, you can hear the the air pumping out of the scavenge stages.
Roots style scavenge dry sump pumps will work so good, that you can eliminate the vaccum pump.
I bought a Moroso 3-vane pump to use with the Weaver 3-stage pump, that I will sell along with old dry sump pump.
Dry sump pumps comes in three different types of gears.
Spur gears, Georotor gears and Roots.