Instead of the garter tab, I began with the method given in devonnejoy’s Pollen Brass and Steam: http://www.ravelry.com/projects/devonnejoy/the-age-of-bra...
I did five repeats each of the stockinette and garter/eyelet sections, then the final garter stitch section, and I cast off as follows:
k2togtbl, move the resulting stitch to the left needle, repeat to the end - see Paula Emons-Fuessle’s video here: https://www.youtube.com/watch?v=cGHItYwr1us&list=UUpp...
(Approx. 86g of yarn used; dimensions after blocking - 20.5” x 53”)