If the head can accommodate the larger screeen, a longer stroke cyl and some mods to the rear holder might do it. Or buy a single head from a challenger or larger gauntlet of similar vintage and slap it on one head.
Let us know what you work out, I think turning an old Gauntlet into a 1 color oversize printer would be brilliant for a machine at the end of it's life, i.e. center bushing going out. <which, as far as I can tell, is the only thing that will ever kill these presses.