I ran 33 x 10.50 on a 15 x 7 rim with 3.75" backspacing without any spacers. With the 35 x 12.50 on a 15 x 8 rim with 3.75" backspacing I used a nut to space the wheel out about 3/4". Wheeled it that way for years.
I guess I am partial to the 8274 on a 40. The Zeon is not so bad, but that mounting plate is not 40 friendly the way it peaks on the corners. Probably made for a heep. 15 minutes with an angle grinder would do wonders.