If the engine comes bolted to a conventional transverse fwd box...it would make perfect sense to retain that for mid engine. Plus they're extremely compact in that configuration. Cooling shouldnt be an issue and with no engine up front you've tons of room for a radiator etc.

And even for suspension, hubs etc...I would always try and use readily available parts. Custom parts are all good and well until you bang a kerb or something and need a replacement. The more OEM parts you can use the better.