As others have already stated only need to add weight to doors to get gap pre-adjusted. I just test fit all the front cap sheet metal, more so for panel alignment (ie. flatness of panel to one another) Incase some tweaking has to be done before body prep. Then just check body panels for gross errors on panel gap meaning will make sure they are close & have plenty adjustments for final assembly. The front sheet metal is the last thing on the resto that goes on after the engine is in (for me anyway). Then I final set the gaps in the front sheet metal. I notice a lot of non concour type shops that mostly do generic Restorations or build hot rods seem to do it like your shop is suggesting. Like stated all cars originally were painted on a body buck without front end in place. Especially in your case where no sheet metal was replaced or damaged. Good luck with your project.