looking for a wheel brake solution

Hi everyone, I've been slowly working away on Leah's Cherokee II and
need to come up with a wheel brake solution. Previously it had a
4.10x3.5 tire. The axle diameter is 5/8".

The Cherokee II, per plans, has a piece of aluminum that gets pulled
down over the tire. This is the way my Cherokee II works too. It's a
decent brake but nothing really powerful, causes a bunch of tire smoke
when you really pull hard on the spoiler handle. Leah's spoiler
handle, however, was not built to accomodate the cables that would run
to such a friction brake. The cable for the airbrake does run past
the main wheel so there is potential to "Y" a new cable off that cable
and install a piece of aluminum. However then there would be side
loads on the aluminum and it just doesn't seem like that clean of a
solution to me.

Oh by the way the 4.10x3.5 tire is 2 ply, probably a go cart or
utility cart tire. So I'd like to get something a little more
robust.

I looked at the Matco website and found this 4" wheel/disk brake that
might do the trick: http://www.matcomfg.com/W40B-idv-2368-33.html I
believe that there is room geometrically for this wheel/brake to fit,
depending on the tire size that goes on it. That leads to one
question about tire specs, is the first number sidewall height and the
second number wheel size? for example a 4.00 x 4 tire would have a 4"
sidewall height and fit on a 4" tire? I used to know that but can't
remember.

I think the 1-26 uses a 4.00x4 tire, but can't remember if they have a
friction brake or a drum brake. I'm sure it might be difficult to
find a 1-26 wheel/brake laying around but it might be nice down the
road to have something that is semi common if i need replacement parts
etc.

any thoughts/suggestions? Thanks!