Certainly I understand all because ETI says it cannot be done does not actually mean it cannot be done. Several years back I replaced my dead generator on a 91 Honda ST1100 with an alternator from a Gold Wing. Honda said it cannot be done. Many older ST's out there running Gold Wing Alternators.
The point here is you have to replace the furnace with one that comes with the bezel and panel. You cannot just buy the bezel and exterior panel. The whole project does not make sense unless you are trying to replace a furnace no longer operating.
I guess someone else can be the guinea pig to try and retrofit, but won't be me.