Choosing scale for train models: what scale is "L-gauge"?
TLDR: Scale for train MOC is a personal preference based on the needs.

Longer version:

There is a lot of personal preferences here. Like, how do you decide if the LEGO track geometry should translate to standard gauge? Why not any other track gauge available in other countries? How do you scale the model if it originally use slightly wider gauge? So there's already some flexibility in how strict you should be considering the scale of your train based on the track gauge.

Next thing is to decide if you want your train to operate within your LEGO city layout or just for the looks? LEGO trains are built in 6-stud wide size. People tend to design their own trains in 6-, 7- and 8-stud width size. They look good in city layouts - not too big and do not cause any serious troubles operating even on LEGO tracks. And somewhat to scale. I've made 48 cm (1.5748 feet) long 8-stud wide scale model of a train loco myself. It could operate on standard LEGO train tracks. And yes, it looks a little ridiculous on curves, but still works. However this scale doesn't let you design detailed interior, so compromises must be made.

Now if you prefer designing your train for the looks and operate it on some train layout (that could be made from LEGO compatible 3rd party elements) only from time to time you can go with whichever scale that fit your needs. It could be wider, longer, so train track geometry is the limit. As you mentioned your initial scaling suggested your train is going to be 2 feet long, which is less than half a foot longer than my model and you are not limiting yourself with just LEGO tracks, there shouldn't be a problem running your model on larger radius 3rd party (LEGO compatible) train tracks.

It is also worth mentioning some people use LEGO tracks as a narrow gauge. In such case train model, is obviously quite wide and it no longer fit into LEGO city (minifigure scale) layout. However there is plenty of space for details.