SR.45 Princess (ID 14164).
TL;DR max cargo weight should probably not be higher than 25,000kg
Also you might consider if you want to have this aircraft at all as I cannot find any references to it actually having internal landing gear.
Beware calculations ahead.
This aircraft is just plain silly. 64 tonne cargo capacity other than being broken for the time is most definitely not feasible.
Yes I have seen sources say that much (well a bit less) but for all practical purposes those numbers are useless.
First off the same sources also list the aircrafts empty and max takeoff weight. If you factor those in you get:
Lets go with what wikipedia lists.
max takeoff weight = 156,501kg (or 3450,25lb)
empty weight = 86,183kg
max disposable weight = 62,142.2kg
max takeoff weight - (empty weight + max cargo weight)
156501 - (86183 + 62142.2) = 8175.8 or just over 8 metric tonnes to spare if we go with max takeoff weigh.
Keep in mind this from what I can find is empty weight not empty operating weight. We have not factored in that the aircraft cannot effectively empty the tanks 100% so our effective fuel is less than that.
Even ignoring that fact do you think you can fly 9225km on that little fuel?
The wikpedia listed fuel capacity is 14000 imp gallons or 63645.3l
Commercial jet fuel is around 0.8kg/l meaning that a full tank is around 50,916.24kg or just under 51 metric tonnes.
Basically filling the entire 62 tonne listed cargo capacity means we only got around 16% full fuel tanks assuming we do not go above the listed max takeoff weight.
Now the intersting part is I found some papers from the ministry of supply from 1956.
These lists the max takeoff weight as just 320,000 lb or 145,149kg.
If we stick with the wikipedia listed empty weight that means we actually only got
145,149kg - 86,183kg = 58,966kg free weight.
That is less than the listed cargo capacity meaning that if we assume both that papers max takeoff weight is right on top of the wikipedia listed empty weight we will exceed the max takeoff weight just by adding cargo.
But wait it gets even better.
The same paper lists a normal landing weight as 250,000lb or around 113,400kg. It is possible to land with the takeoff weight in an emergency but you would not do that in normal operations.
Again sticking with wikipedia for aircraft weight that means we only got
113,400kg - 86,183kg = 27,217kg free landing weight.
Note that has to include some fuel unless you want to land it as a glider.
My recommendations is that he princess should not have more than 25000kg cargo capacity. Maybe a bit less.
Also just for the record I cannot find any references to the aircraft actually having any landing gear (all pictures show it having them attached externally) meaning that from a practical perspective the aircraft would not be able to land at a normal air field.