After a hard look at all the pieces, I found an answer that will give me another 7/16" total room with the belt driven fan, and 5/8" if I use a pusher electric. Although it may seem like "not much", it's a bunch when it means the difference of either major firewall work, or moving the radiator.

I have a "dog dish" two grove WP pulley which overall is shorter by 3/8" than the single scheave unit in my Elco, which uses the front scheave on the balancer, and I use the back groove to drive the alt on the '37. The groves measure 5/8" accross. The back of the WP drive flange measures 21/32" to the seal. If I press the drive flange back 5/8", I can remove the rear belt scheave from the pulley and drive the alt off the front groove. I'm concerned that 1/32" isn't enough clearance , so to make sure I'll press the drive flange off and machine it, facing the front and taking some off the back as well. I'll need to do two pumps so I've a spare. The fan I have will need to be spaced out 3/16" to clear the balancer and t-stat housing when everything is done..

If all the numbers hold up, by putting the engine closer to the firewall than the stock 216 was, I end up with 3/8" more room at my aluminum radiator than the 216 had, using a belt driven fan, and have room to change the belt. YES!!!!!!
'37 Master Deluxe 2dr sedan
'66 Elcamino, 250, 3sp OD