Hi Scott
The source of the info on ....
McKenzie Alexander 00-11-1914 Ardrossan, 57 Kilmahew Street
McKenzie Alexander 00-11-1914 Saltcoats, Canal Street
....is the Glasgow Herald/Evening Times Roll of Honour, but these can't be your man as this Roll of Honour commemorates those who died in WWI.
I assume that you've had a look at the Medal Cards on Ancestry. There's a very tempting entry for an Alexander McKenzie who transferred to the MGC on 26Oct1915, but he'd first served in the 1/6th Gordons, - the Banff and Donside Territorial Bn, - and there's a thread on
http://1914-1918.invisionzone.com (The Great War forum) that identifies him as having been born in Dyce.
The local paper is the Ardrossan & Saltcoats Herald. While they do have some indexes these, so far, are only BMD related. You're quite correct that may well be a reference to a local man having signed up with ......
... the 'natural' regiment for a man from N Ayrshire would be the Royal Scots Fusiliers. Given that he enlisted early on it's more than likely that he went for his local regiment; but then, if his parents were from "McKenzie country" he may have gone for a regiment local to that area. If they were from Ayrshire, then the RSF has to be the favourite.
Medal cards are reasonably reliable in terms of showing transfers, and there's no records where an RSF man transferred to the MGC (actually I think there was one, but it was one of the small proportion where an address was shown on the back and it wasn't anywhere near N Ayrshire!).
I can confirm that there are no obvious matching pension records or service records. As regards the former only a small proportion of men received a pension, and most often only if they had been wounded, - that included being gassed. These records have survived in their entirety, being stored in a different archive from the service records which were partially zapped by the Luftwaffe in WWII.
Some expert somewhere may be able to identify for you which company of the MGC served at Hill 60, Ypres, and Mons. BTW, see
http://www.ww1battlefields.co.uk/flanders/hill60.html for info on that location.
It could be worth researching this action further to see what info is available on MGC Cos. involved.
If an MGC Coy. can be identified then there may be a surviving War Diary for the unit. At the battalion level there is a high survival rate of war diaries, with an ever increasing number coming on line via TNA, but I have no experience as regards war diaries for the MGC.
A query on
http://1914-1918.invisionzone.com could be worth a punt.
Orraverybest
David