So I took the 1606 shell off the F3 and made some mods, like putting the Kadee back on and removing some extraneous electronics (the battery harness and the smoke unit, et. al.) and took the shell from the non-powered 1607, swapping the melted number boards for a fresh set from Lionel.
This will now be the trailing unit with the new 1606 becoming the lead. Of course the coupler cover will be closed on the 1606.