Use your old water pump - if you just changed it - yard engines water pumps fail quick. The oil pump and sump are different on 203 and 210 - yes you will need to swap your old items but please check the pump itself for wear - do not install a bad oil pump.
Do not use any rtv on the sump gasket as it will leak. If you need something to make the gasket stick - hylomar blue is the best!!! - I use it on BMW sumps too which provides an extra sealing (which I like because they leak like stupid when at half age)
run a thread chaser in all bolt holes on engine and renew any disturbed oil rings, Use viton or HNBR if you can. Plain old BR rings also work (they were original equipment)