OK, authenticity I can see. I was thinking more practicality. Narrow gauge track on standard gauge ties would work just fine, and take less effort, which seemed like a good idea.
Incidentally, my Nn3 track uses 7'6" ties, by accident. I ordered "old time" standard gauge ties from Clover House, supposed to be 8' long. Two packages were only 7'6", so I used them for my 1974, coal and ore hauling, narrow gauge. Nice to know the EBT used the same size!