Driver / Horn mismatch issues with MT122

We built a couple of MT122 box, now we have the following problem/question.

A while ago we've bought 4 B&C 700 8 ohm compression drivers, we're planning to use them in the MT122 box. This means we need to find a good horn with a 60/40 dispersion and the right dimensions to fit it in the box.

The problem is that B&C only made 1 horn for this driver (we mailed B&C about this). They advised the following horn B&C ME 90. The problem is that its 80/60 dispersion and the dimensions are to big, so it wont fit in the box. 

We're looking for a good alternative horn to use on the box with the driver. But we're thinking that most horns won't fit due to the mounting screws which are in a different position. Next to that the specs of the driver say the driver has a 1.5 inch horn, when we check specs of the ME 90 horn we see this piece of text "can be used for 1,4" driver, e.g.. : B&C DE700/900". Because we got confused we decided to measure the throat diam ourself and we measured 1.4 inch...

We've found a horn which would fit the box good, but we are not sure of this horn would work with the driver... http://www.bluearan.co.uk/index.php?id=PAUPH3022&seeimage=YES&img_name=ph3022

any idea on how to check/calculate if those work or even fit together?

Although i fully agree that that specific horn is very good, it's even bigger(both width and height) than the ME90 which the OP said was already too big.