A few thoughts - most of them have been expressed.
A 30 series converter will last fine on a stock 212 if it is PROPERLY installed, PROPERLY geared for the weight, tire dia., and a QUALITY belt is used.
That said - You do not need to install a new engine with a 1" output shaft to use a heavier duty 1" 40 series converter set-up.
Many of the kart supply sites offer 3/4" - 1" adapter kits specifically to do this.
A jackshaft can be your best friend in optimizing gear ratio. While it is a little more expensive and takes more effort to install at first, it is then usually easier and cheaper to change ratios later. One big advantage is you can use a larger output sprocket on the converter for more chain tooth contact, resulting a longer lasting chain. Another is you can use a smaller (and cheaper) axle sprocket for more ground clearance.
