Ok, 1... Coocooloco is nutz, that's not a Express... his is a Pinto with a frame brace. A LOT stronger.
If you add a frame brace to the express, it'd look like a BMX bike! I'd do it!
I just think you need to look at the transmission... it's a sealed unit with a jack-shaft type setup. There IS a chain in there, and some-sort of sprocket... but I'm not sure they make aftermarket gearing. You could probably find something that works though.
I've personally never opened my transmission on my Express, only changed the oil.
Hrmmm. Now this has me thinking. Frame brace, Beefier front suspension... longer-travel rear suspension... could have a small off-road scooter at best... that damn transmission casing is too Scooter-esque to do any real off-road mods...