Thinking about mounting it to the engine lid with some louvers fabbed in to the lid itself.
Mounting in the engine cover will work, with a couple of caveats...
as the engine cover is one big vent, putting the cooler on there will mean you will also need a thermostaically controlled fan.
Air, just like water or electrons, will always take the easiest path. If it gets the choice of of passing thru a closely spaced matrix of a cooler or the wide open spaces around it, it's going to go around. so it will need to fan to ensure sufficient air is made to pass thru the matrix.
It also means ensuring the hosework is long enough to allow the engine cover to also open freely, without also putting any strain on the cooler or fittings. That's what will kill an oil cooler (well that and a stray stone) and I've seen a few cracked and split from improper mounting. t's also really important to put a spanner on the cooler "nut" when you tighten the fittings up, it's very easy to twist/bend the end plate and ruin the cooler.
Included in the Mocal 19 row cooler I just bought is a slip that basically says any cooler more than 13 rows must be mounted at all four corners to properly support the core or the warranty is simply void. They also recommend using some form of rubber isolator if the installation will be subject to vibration, which I'd guess in your case would also be a good idea.
Cooler / fan / mounts / hoses all weigh something, and that weight in the lid (affixed to it) will mean a well thought out mount is needed.
Fitting the cooler and fan to the body and having the lid close down onto it creates access issues to parts underneath it, so I see the appeal of having it fixed to the engine cover and swinging up out of the way.
If you use hose to plumb the system, and not hard line, you need to pay attention to the hose type and the total length used, somewhere for the hose you choose you will find a table of flow / pressure loss related to length / hose I.D. size so it's important to size hose and fittings appropriately. Resistance to flow is tied (mostly) to the speed of the fluid thru the hose ID, and the losses do an exponential curve as speed hits around 2.4m /sec with most fluids of around the viscoscity / S.G. of water, small ID fittings and smaller ID hoses flow fast and cause a lot of pressure loss.
SteveC