I cannot answer the tank size question directly. These boats were low production units. DOn't know how many were actually built but not many. You can measure the tank height, length and width and calculate.
277.8 cu. inches per Imperial gallon, 231 cu inches per US gallon by my memory and then looking at a calculator page to confirm memory is ok yet.
If you measure the tank exteriors then you can calculate the gallons, both US & Imperial. Measure carefully as some tanks may be tapered front to back, end to end,
Don't assume the gallon capacity stated is Imperial. It may be but you should confirm that yourself or you could get a nasty surprise one day.
Boats built in Canada often quote/quoted USG capacities.
Of course tank wall thickness will change that but so little it can be ignored.
I had to do the same a long time ago and I'm glad I did. Different boat of course.