Not really surprised that the CG calculator says 60% Colonel, with that big a lifting tail. 40% should be ultra safe, if it comes a bit aft of that with your preferred lipo position I wouldn't worry.
Re Free-Flight Supplies and Mike Woodhouse. I can only echo your sentiments, I have been buying tissue and mylar from Mike for - what, it must be 15 years now - and his service has never been less than absolutely excellent, as are his products. He also happens to be one hell of a good modeller, which may explain why he cares about what he supplies.
Is the stuff you might be forced into using for the covering water based? If not I wouldn't be sure how it will turn out. You could try Poly-C (http://www.rcworld.co.uk/polyc.html
), this is £10 for 500 ML, still a lot more than you will need for the Ajax, but I get the sense you may be building others? As far as I know this works just the same as the water based urethane varnishes I have tried, they say it has "an adhesive" added, but I don't know from personal experience. Of course, you could always lay new hardwood floors in the house, then you would need to buy litres of the stuff on the household budget and there would be sure to be some left over, that's what I did
PS: I thought it was expensive here in France, but the brand I use, 3V3 is "only" 65 euros for 2500 ML, which at current exchange rates makes it a bargain compared to your £25 for 750 ML!