200b to 240k compatability?
Well the IRS may have some similarities for starters.
The L20b 4 cyl im pretty sure shares the same timing components as the L24.
Suspension and brakes will depend on the year of the 200b, as im pretty sure the earlier ones had Japanese type calipers and mounting holes, then the later ones had Aus calipers (or ones readily available in Aus)
And yes, they are not the comfiest or most economical, but are getting rarer each year, and cool factor / retro status is increasing.
Power wise you have 30 plus years of modification options! Tripple carbs, dual carbs, big singles, EFI and turbo.
My choice would be to find a wrecked MR30 skyline (factroy efi, high compression, better fuel economy if tuned well)
and pull the engine & running gear from that, slot into the 240k.
Although thinking outside the box is something not done too often with the 240k, like a diesel conversion or rotary! (sr20det even....)