Sadly I am not qualified to say anything about what fitted to what and when as I barely know wot-iz-wot having only been up close and personal with the one Scott, (or parts of many?). For example my 1950 (alleged) box-o-bits has a short frame mag/dyno, (wot no coil/distributor?), it also came with two gearboxes with different ratios both of which would seem to be intended for hand-change although one has a crudely attached foot change selector sawn off something else.
I hate to see grown men cry so I won’t go on.
On the subject of fuel heights the following might be of interest:
I have a tiny side valve engine designed by Edgar T. Westbury, a name that will be know to all model engineers and it is said the inspiration for the central character in Nevil Shute’s “Trustee from the Toolroom”. It was intended for use in the field during WWII as a small generating set. The carburettor has no float chamber and has to suck the fuel up some four inches from the tank that forms the base of the set. This it does with some alacrity even when hand starting from cold.
As I have said before it is quite hard to have the fuel height too low! Logically, when you think about it, the fuel head need only be sufficient to keep the main jet submerged at full throttle.
As Richard says check the condition of the float needle and seat.
Take the top off the float bowl and see if the needle seals when you blow down the top connection.
As far as the needle seat is concerned I’d be inclined to go for a thin line rather than a matching taper, greater pressure per unit area plus less area for foreign bodies to get stuck to.
Also make sure the float chamber is set vertical.
If it still leaks try inserting a light spacer between the float and the needle clip and see if that improves matters, it might give some clues as to what is going on.