Why would you want to go a top mount? Front mount is a much better setup, less heatsoak from the engine, much more effective in cooling intake temps. There's a reason most Jap and Euro imports have front mounts (Skylines, Rexxy's, Evo's etc etc).
It can be done, but you will be doing a lot of work and spending a lot of money for less gains. You will need a mount made for the cooler on top of your engine, piping will need to be bent up for it to suit, cut a hole in your bonnet for a scoop etc etc. Bit of a waste of time for nothing.
If you want a hectic bonnet scoop for your D40, just cut a hole in the bonnet and bolt one on and pretend you have a top mount lol