Graeme,
There is nothing specific in the rules to cover this question. However in the open discussions a couple of months ago, the question of multiple entries was discussed at some length and the end result was to whittle down the suggested 4, to 2 entries each for a trial period (including this current Quarter). There is also a restriction on editing techniques, which again doesn't specifically cover this point, but to me, your proposal is outside the term "Basic editing" although I can concede that it could be a fine dividing line. With only 3 days to go, there isn't really time to get wider opinions, and to allow it now would potentially disadvantage other entrants.
So the "editors decision" is that for this quarter your proposal won't be allowed I'm afraid, but I'm open to comments from anyone as to whether the rules should be adjusted for the future.
Rather than your montage, may I suggest that you simply select your two most favourite shots and enter those individually, which is permitted under Rule 2.
For reference, the 2 rules to which I've referred are :
2) For a trial period, each registered forum member may submit TWO pictures, and those pictures may be replaced up until the closing date. Each picture must have a Title and if two pictures are submitted they MUST both be on the same post.
5) ....Basic editing will be allowed. i.e straightening, cropping, resizing, but advanced techniques such as adding smoke or steam effects, adding background pictures, etc, will not be permitted. This does not exclude for instance, using temporary physical screens to hide unsightly backgrounds before taking a photo.