I have two old vehicles with vacuum wiper motors, and from my experience I think either way will work. I have a 57 Buick running off the manifold, and it works just fine. When I rebuilt my 53 truck I put a fuel pump on with a connection for wiper vacuum. It works fine also.
As a practical matter, unless this is a truck you use for regular transportation, you will probably almost never use the wipers anyway. I don't imagine you drive your toys in the rain unless you get caught out somewhere and have no chioce, so either one should be fine.
The big outlet for the vacuum was for the hydro vac, and the two speed rear end, if the truck had those items. Only the larger ones did.
Allen
