Originally posted by Streets
Could have been Matt...

Ad in a mag of old time chevvy parts:
We have every Chevrolet fuel pump in stock, ready for immediate shipment. Many applications used “dual action” pumps which have a vacuum booster for the windshield wipers.
1942-51, 6 cyl optional w/ vacuum 9126 $139.50 $25
1952-54, 6 cyl fuel only 9798 $59.95 $5.00
1952, early optional w/ vacuum 9803 $139.50 $25.00
1952, late-54 incl. 1953 Corvette optional w/ vacuum 9797 $139.50 $25.00
1955-57, all 6 cyl fuel only 4149 $59.95 $5.00
1955-57, all 6 cyl w/ optional vacuum 4138 $139.50 $25.00

But, the point is moot as you can use vacuum
from anywhere on the engine, they used the fuel
pump because it was a constant supply regardless
of intake manifold vacuum changes

Suggestion: IF you want a constant vacuum supply
where the wipers don't slow down upon acceleration,
then use a Vacuum cannister setup similiar to a
power brake booster or cruise control unit (Vacuum tight coffee can)...
Thanks Streets, how do I hook the coffe can into the vacume line?