This is a table for weight, ST, and Movement, scaled to 100 lbs, ST 10, and Move 10 at SM 0.
ST is scaled linearly with length, movement is scaled with the square root of length (which isn't entirely realistic but it gives numbers that aren't crazy).
To scale a dragon from one size to another, take it's measurement at it's current size, divide by the table value at that SM, and multiply by the table value at the desired size.
Example:
An SM+5 Dragon weighs 50000 lbs, has ST 88, and Move 15. The same dragon, scaled down to SM-7, weighs 0.05 lbs, has ST 1 (1.17, if it matters), and has move 2 (1.67 if it matters).
The same dragon, scaled down to SM-3, weighs 5 lbs, has ST 5 (4.7 exactly) and Move 3.
I don't think DX, IQ, or HT is going to meaningfully scale with size.
Code:
SM Weight ST Movement
7 337500 150 39
6 100000 100 32
5 42188 75 27
4 12500 50 22
3 4287.5 35 19
2 1139 23 15
1 3378 15 12
0 100 10 10
-1 42.2 8 9
-2 12.5 5 7
-3 4.29 4 6
-4 1.14 3 5
-5 0.34 2 4
-6 0.1 1 3
-7 0.04 1 3