I've got a 16 inch SPAL sitting at the shop for my T. I'll measure it today for you.

Mine is a little tight too ( I should have allowed another inch or so in frame length when we built it) but the fan tucks up nicely in there, as the plastic housing is pretty shallow on the outside, and tapers in only a little to the fan motor.

Sounds like you have a workable solution going on.

Don