While I’m not familiar with the particulars with the Y swap into a ’50 Ford, here are my thoughts on the front pulley situation assuming the pulleys must be spaced further forward.
In lieu of using the one inch spacer behind the water pump, the pulley can be spaced out further using a fan spacer between the pulley and the water pump. As far as the Thunderbird damper part of the equation goes, an alternate option would be using an Innovators West harmonic damper. While I am working on the design for a damper specific to the T-Birds, the current IW passenger car/pickup offering can potentially be made to work by using a small block ford belt pulley or using a spacer between the Innovators West belt pulley and the damper. Here’s a picture showing an Innovators West damper offering using a 7/16” spacer between the damper and the lower pulley to align the belt with the w/p pulley. The water pump is already spaced out using one of Frank Rice's Thunderbird water pump spacers.
In the near future, Innovators West will be able to supply a bolt on Thunderbird damper and single belt pulley combination that will require no belt modifications when used on the Thunderbirds.