Initial findings.
Valve Springs3SGTE = 43.30mm L, 27.00mm OD, 20.00mm ID, 35 gram, 23.00mm bind*
1MZFE = 45.60mm L, 24.10mm OD, 17.90mm ID, 28 gram, 22.90mm bind*
* Bind being when I cannot slide a sheet of paper between the middle most coils when the valve spring is compressed in a vice.Buckets1MZFE = 25.55mm L, 31.00mm OD, 28.95mm ID, 46 gram
3SGTE = 25.30mm L, 31.00mm OD, 28.95mm ID, 37 gram
1ZZFE = 25.25mm L, 31.00mm OD, 29.30mm ID, 29 gram
Well they all match in sizes within useable tolerances and it looks like they are indeed interchangeable. Will find out more when I actually try to fit them into the 1MZFE.