would like more power from 240 dont want to go to bigger engine. is 200hp possible without the loss of tractability and reliabillity? Over optomistic? too expensive? What could I expect with worked head, cam and extractors?

Live in Australia so limited avaliability of stuff ??

depending on what year you have you can get more. my 72 ran like a bat outta hell with a .40 overbore, e88 head with bigger vavles, 480 lift 292 duration cam, and headers with exhaust and a 5 speed. i cant imagine what it would have done with a greater rear underneath it

200hp is possible out af an L-24 but it is going to cost a lot more than you may be willing to spend. Here in the US, Rebello engines is charging 4-5K for their racing engines with that kind of hp.

You might get 20-35hp with head work, cam, carb and exhaust mods. The easiest and cheapest solution to getting near the 200hp range is doing these mods to an L-28 with the early carbs and intake.