I used one off a Citroen BX (it was scrap, even before I started on it !) which I found fits perfect in the ledge at the bottom of the radiator on my '91 V8. I made a small bracket to brace it to the top bar and that's all it needed ! few wires and a relay and that was it - took far longer to get the nut on the old viscous fan off :(
I've not put an automatic switch on it yet, just got a lead to the cabin. In normal driving it never needs to be on, airflow at 30mph is enough to cool it (and it was at the end of August too) I just flick it on when I get to a lane. As Miniman suggested I switch it off going through deep water too.
Well worth checking around the local scrapyards, will only cost you about a fiver then.
Cheers