The trouble with Accusumps is......

..... that they may not always fit under the bonnet! Well nearly but not quite. I have to admit to have taken a flyer with the positioning of the Accusump. The height of the installation was measured relative to the header tank. However, looking at the underside of the bonnet it was clear that I hadn't bargained on the deeper edge to the bonnet:
With some careful setting out it appears that the body of the Accusump will fit - it is just the pressure gauge that fouls the underside of the bonnet. The easiest fix will be to remote mount the gauge.... time to order some more plumbing bits then.