OK, I looked at the dimensions of the New Horizon plates on their website and and made a wooden mock-up of the standard one. It appears to fit my Klose 20x48, so I went ahead and ordered it. I will test it when it arrives without, with, and with plus a 1"-2" gap. Results to be posted here.
Klose 20 x 48, Stainless Performer, Smokey Joe Platinum, stainless hibachi, coal rotisserie, cinderblock hog cooker