What is that hockey puck shaped cannister just above the oil filter on MEL engines ? Is it an oil cooler ?

The bell shaped piece on the oil filter adaptor? That would be the oil pressure sending switch.

If not, what is your application?

Power Steering Resevoir?

The cannister in question is not part of the oil filter adapter, its farther up, its about the size and shape of a power steering resevoir, but Ive seen it in illustrations of MEL engines that have no power steering or air conditioning ( only water pump and alternator ).

Some installations (LINC-MERC) had a crankshaft driven P/S pump. The reservoir is smaller than the belt driven Eaton pump and is bolted to the the front engine cover tucking it in close to the engine. The photo shows the pump on the right and the reservoir on the left. I don't have an installed photo at this time. Look familiar?

Thanks, KULTULZ, for solving a mystery to me !