I just installed the riser block this weekend. The instructions call
for a 26mm combo wrench. I could swear I used 15/16" (don't have a
metric that large) and I just fit it over the bottom nut (it was
loose), which does look a tad smaller than the bolt head (behind the
switch now so can't check it). I used a crescent for the other
(thought I used the 15/16" on the upper though) end.

There is clearly room for a crescent wrench on the bottom (nut end) and
maybe on top. You could definitely fit a channel lock plier over the
top end of the bolt. So that would save you buying any combo wrench,
assuming you have a crescent that can open 1".