For an engine crane - it's more economical to buy one over here. Cost of parts tends to exceed the cost of a ready made one. Mine is a 1 tonne folding Clarke and has stood up to lots of abuse over the years. Don't know if you can get anything like that over there.
Go kart covers a mutlitude of sins, design depends on use (onroad, off road, race), engine, physical size etc etc. If its just for fun the best way is experiment, have a look at the stearing geometry on a bought one and just go for it!
not exactly a gokart but a project I'm going to undertake in the next month or so... http://www.amazon.co.uk/Build-Your-Own-Off-road-Buggy/dp/1859606423
give some good advice/ideas and would be a great starting point for anyone who's not so familiar with the principals of building this kind of this (like me)