Dear Michael,
With all due respect, I have to disagree with your calculations.

First, let's agree with our starting measurements for a M3A1. Various tank references have slightly different measurements for this Stuart tank (Hopefully Gary B. can say what reference is most accepted):
1)
The Encyclopedia of Tanks and Armored Fighting Vehicles - The Comprehensive Guide to Over 900 Armored Fighting Vehicles From 1915 to the Present Day, General Editor: Christopher F. Foss, 2002: W: 7'4" or 2.22m, L: 14'10" or 4.54m, H: 7'7" or 2.3m
2)
British and American Tanks of World War Two, The Complete Illustrated History of British, American, and Commonwealth Tanks 1933-1945, Peter Chamberlain and Chris Ellis, 1969: W: 7'4", L: 14'10.75", H: 7'6.5"
3)
Tanks of the World, 1915-1945, Peter Chamberlain, Chris Ellis, 1972: Same authors with two measurements slightly different: W: 7'4", L: 14'10", H: 7'6"
4)
The Encyclopedia of Weapons of World War II, Chris Bishop, 1998: W: 7'4" or 2.24m, L: 14'10.75" or 4.54m, H: 7'6.5" or 2.3m
5)
Jane's World War II Tanks and Fighting Vehicles The Complete Guide, Leland Ness, 2002: W: 7'4" or 2.24m, L: 14'10.75" or 4.54m, H: 7'6.5" or 2.3m
6)
Tank Data, World War II, Aberdeen Proving Grounds Series, 1969: W: 7'3", L: 14'8", H: 7'5"
Using the most repeated measurements, I will use W: 7'4", L: 14'10.75", and H: 7'6.5" and first convert them to inches: W: 88", L: 178.75", and H: 90.5".
Now, 1/30 scale is the above measurements in inches divided by 30 and 1/32 scale is these measurements divided by 32:
1/30 scale: W: 2.9333", L: 5.9583" and H: 3.017"
1/32 scale: W: 2.75", L: 5.5859" and H: 2.8281"
Now, measuring my Figarti M3A1: W: 2.75", L: 5 9/16 or 5.5625", H: 2 14/16" or 2.875" so I would have to conclude it is very close to a true 1/32 scale.
My K&C Stuarts are all currently stored, so I will use your measurements: W: 3.6", L: 7.6", and H: 3.6". These measurements make the scale of this vehicle closer to 1/24 scale if you accept a 1/30 scale M3A1 Stuart has dimensions of W: 2.9333", L: 5.9583" and H: 3.017". I am wondering if you measured your DD067, which is a M5 model or included the length of the hedgerows. Hopefully, someone else can provide measurements of their K&C Stuart since I do not think K&C's scale would be off so much.
Finally, I hope everyone notices that the difference between 1/30 scale and 1/32 scale for a M3A1 is less than 1/4 an inch for width and height and less than 1/2 an inch for length, which is probably why many collectors say the Figarti Stuart goes well with their K&C Stuart.