I agree it would be more to drool over however I am in the process of building a model drilling rig for my father as a retirement gift and will need to design some sort of transmission.
On a real rig they use a 6 speed diesel transmission similer to a large trucks and I think the t-5 would be...
Sorry if its been asked, do you plan on releasing downloads to all pages of your plans? While near impossible to replicate I think the mechanical aspects to the transmission on paper would help to adapt to custom build model transmissions. Without taking apart a t-5 or similar in the garage that is.