If it was me there is no way I would spend the best part of £30000 on any product that did not meet my expectations especially if I had waited ages for it. You will regret it from day one till the day it goes.
Either walk away or get the dealer to order in exactly what you expected.
I try to get my cars from dealer stock with huge discounts. Got £3000 off when I bought the Leon which more than compensated for the lack of Climate and privacy glass I would have insisted being fitted on a factory order. Wife recently got £4000 off a Nissan Note that was in dealer stock. Considering a Pulsar next and already spotted over £7000 off those.
Just looked on the Broadspeed site (a broker I have used in the past and will probably use again). You say that "The only discount they can offer is £750 scrapped from many barrels." yet Broadspeed are offering over £5000 off the
290. So definitely cancel your order and reorder elsewhere getting a huge discount and exactly what you want.