Ideally you should have someone at hand to help if needed, its a heavy item and a pain to support it underneath and line the bolts up.
Also to get it out, you will have to drop the coolant rail which is the metal pipes running along the front under the rad, they contain a drain plug for you to drain the coolant first, but these are known to be very tight and can round of easily so use a 6 point socket on it, if it wont come out then simply drop the coolant by removing the lowest coolant hose of the rad.
I did try to get mine out without removing the coolant rail as I had recently renewed the coolant anyway due to water pump replacement, but no matter how much I fiddled, it would not come past the coolant pipes. So your going to need some OAT coolant as well to refill the system upon completion of the steering box.
Also, the drop arm can be a real nightmare to get off, often they have to be cut off, so if your new box has one on it then thats a lot of potential headache removed from the job. Paddocks recon boxes (for example) come with a new drop arm.
Out of interest, did you look at paddocks for a recon box as they are no where near £290.......they are only £214
+ vat but that includes £100 surcharge which you obviously get back when you return your old one.
http://www.paddockspares.com/pp/DIS..._includes_100.00_GBP_exc._VAT_surcharge).html