Lots of posters on here seem not to be happy with the stock brakes? I can see that improved drum brakes, would certainly mean the stock chassis and forks, may well not be able to cope..............thanks for pointing that out!

Yes, arcing the brake shoes is(was) common place for auto drum brakes at a decent brake shop.  Any shop that still has the old drum lathe can probably do that for you.
If brakes are aftermarket or poor fit, you might just have to advance the lever to lead the cam and cause it to ramp up quicker, but you'll have to have enough slack in the cable. If that is the case, they probably also need to be re-arced.  If there's not enough slack to do this, the shoes are probably right sized.  Also check how worn the actual lining inside the hub is, and not contaminated, and check for wear and size of both the cam and fixed pin on the backing plate.
Have someone familiar with old bikes ride it, you may be expecting too much if you've only ridden with disc brakes.  You're not going to lift the rear tire unless you go to double leading shoes.
 

The main reason drum brakes in most cases dont work that great, is the lining material used. Upgraded linings, mean better brakes.