This sounds kike a trivial question, but it gets asked a lot. What size is the condenser mounting screw? Adding to the confusion, all of the MGA Service Parts Lists have the illustration of this part, but none of them have a part number for it. This screw should be a 4BA cheese head screw (Whitworth 55-degree thread standard). Thread major diameter 0.142-in (3.6mm) . 38.5 threads per inch. If you need to get something assembled in a pinch, a #6-32-UNC screw is pretty close with 0.136in major diameter and 32 threads per inch (60 degree threads). The small difference in thread pitch won't be noticeable in such short thread engagement length, and you may likely get away with it being 0.006-in smaller diameter.

In this illustration item 3 is the condenser with the mounting screw with lock washer just to the left. Item 4 is the points and condenser mounting plate. The condenser fits into the rectangular slot with the screw hole at one end of the slot. That's all you get in the SPL.