Didcot's Siphon G has **never** been restored - just repainted & the roof canvas replaced with roofing felt back in the 70s (& re-canvassed properly when it was repainted a few years back).
The amount of glossed-over kack on the underframe ought to be obvious testimony to all who have eyes to see. If any rebuilds have occurred, then they'd have been in BR days & ought to be verifiable by referring to the appropriate Register.
Russell Coaches Vol 2:
Fig 308: 2992 L.1644/1945 - Offset 'independent' cylinders, lever brake, central batt boxes.
Fig 390: 2792 L.1578/1938 - Cylinders inline, DC lever, central batt boxes. Photo ex-works as built.
Russell Coaches Appendix Vol 2:
Fig 522: 2937 L.1644/1940 - offset 'independent' cylinders, lever brake, central batt boxes.
Fig 523: 2796 L.1578/1938 - Cylinders inline?, DC lever, central batt boxes? BR era photo.
RC 2 also has a Weight Drawing dated 7/1930 covering Lots 1441, 1651 & 1664 (so presumably amended over the years):
Lot 1441 - 7'-0" Bogies, 35'-0" centres, 49'-11" over headstocks, 53'-7" over buffers.
Lots 1651 & 1664 - 9'-0" Bogies (except for 4 unspecified fitted with 8'-6") 34'-6" centres, 1/2" smaller than L.1441 over headstocks & over buffers.
As to the model... since Minerva are planning on including the little slidey hatches from that suggests they're trying to find common ground between O.33 & O.62 - Good luck with that (unless it'd work with separate add-it-yourself battery/regulator boxes in addition to the vents)
Oh, and @mountaingoat - Please, it's Siphon, not Syphon.
Pete S.