Agreed, the grub screws are simply there to locate the chokes / venturi's and don't need to be tightened as much as these obviously had been at some point.
If you replace the carb, you need to locate one of the same type. i.e. Webers have the type stamped on top, Solexes have a metal sticker with the part number, though this often falls off, or becomes illegible.
For solex info, talk to Rodger http://rmcarburetors.net/