That’s fine if you are an ‘average’ sized person – average to the nation of manfacture that is, though the smaller framed orientals have made their machines fit all – there comes a point when some personalisation can be beneficial to comfort and desires. Some changes will require cutting and/or welding.
Reed valves. Buy a Yamaha. Leave as designed with regard to the MZ. Two strokes can be tuned, but you steal from Peter to pay Paul, same goes for any engine tuning for more power, there inevitable will be a price.
Welcome to the club Ian, can’t help much more than that.