JoeD, this may seem a little primative and others will probably chime in. To check which distributor you have just take off the cap and try to turn the rotor. If it will not move in either direction it's a Loadmatic. If it will move in one direction about 10-12* it is a centrifugal, which is 57-up. Also stick a long enough hose on the distributor can filling and suck on it to see if the plate moves, if it does that will prove your vacuum can is working. If it will stay moved with your tongue tip over the end of the hose the can is good.
Your truck is a 1960. I cannot believe your dist is a loadmatic.
 As Ted stated the Merc WCFB's were used with loadmatics in 55-56 and were not compatible with the 57-up distributors that's why I first went to the GM carbs because they were. 
There were many of the guys I knew back in the 60's who ran their distributor vacuum off manifold and not ported and made them work. The engine would always idle faster and the just turned them down. Others ran no vacuum and set the advancing springs as light as possible and kept total advance around 34-37 degrees and just lived where initial advance showed on the balencer. We were just kids, what did we know anyway.
We all have ideas that seem to work. Eventho I'm a California guy I've met Ted and watched him do dyno pulls (thanks to Karol Miller) and he has done more tests and ran every combination known to man on a Y-Block and I take his word as gospel. He and so many others on this site have helped me iron out problems which have never happened to me before and cannot thank them enough.
You will figure this out.