Thanks for the comments, one and all.
@Dan_L - I have run the fans for a while and looked at the current draw, which is indeed just around 4A. And you're right - this puppy pushes (in my case) around 400-450cfm of air according to the spec sheet. I will consider relays if the wiring takes a hit, but right now there's no sign of an issue and all wires, switches and connectors remain nicely cold.
WRT to positioning, it would have fitted behind the faux grill, or even of course in the under-bonnet area as well, but at that distance the effect of the air stream was slightly less (primarily because the air comes out in a cone shape and widens it's area with distance, so I wanted the fan as close to the engine as possible. That it is still pretty much hidden to most eyes even on the outside, made that an easy decision for me.
Re: the amount of air - it's pretty good actually and the hot air that gets forced through the engine and only your knees in front of the car is pretty significant (whilse wearing shorts, obviously....), so I am sure it will help. It's certainly much better than nothing.
WRT under-bonnet -ve pressure - that area really isn't sealed sufficiently well to make it a problem, as there's loads of access from the outside world in towards the fan around the bell-housing at the front of the chassis. It clearly does 'breath' well, as the exit air from the cowling is pretty warm, so it sure gathers energy as it passes the hot oil tank on its way through.
Were it not for the fact that the fan blade needs turned round as well as reversing the connections, to make it suck or blow, I'd rig up some method of making it directionally switchable, to blow oil-tank-heated air onto my feet. But as that's not possible, I'll just have to man up and wear more socks this winter!
