instead of spending $10 or so on 2 sachets of safale yeast, try just one sachet of safale yeast and making a yeast starter out of a bottle (750ml) of cooper's dark ale. you'd have to prepare that in advance about 24-48hrs but it should be good.
for the liquid amber kit, you could just put together (measurements for a 22.5L batch) 500g Dark Liquid Malt, 500g Light Liquid Malt, 500g Dextrose, 250g Maltodextrin.
however, if you are feeling really adventurous, you could knock out the dextrose and substitute it with your favourite malt powder or liquid type. or, you could even substitute just some of the dextrose, say 150-250g of it and use a bit of crystal grain. maybe that's getting a little hectic though...
remember, that malt powder does not use the same measurements as malt extract liquid:
malt powder contains roughly 1.9% alcohol per kg.
malt extract liquid contains about 1.6% alcohol per kg.
dextrose contains 1.8% alcohol per kg.
the maltodextrin is there to give your beer a bit more body and head retention only if you are using that 500g dextrose configuration. you could always add a little to an all malt though if you like it full.
personally, if i were to make the brew, i would do the following:
(1.7kg) 1 can of Cooper's Dark Ale - i'd keep the yeast and use it too
(500g) Dark Malt Extract Liquid
(500g) Light Malt Extract Liquid
(250g) Maltodextrin
(250g) Crystal Grain
Yeast starter made from 1 x 750ml bottle of cooper's dark ale (2 if you are making double. lots of yeast is good if it's good yeast). if you are using double the ingredients though, put in the 2 x 750ml starters, but only put in one of the two yeast sachets that come with the can kit.
now, i'd boil in some golden cluster, goldings or fuggles hops for about 5 mins with some of the malt to balance out that huge amount of sweet wort. i'd use 12-15g of golden cluster and boil for about 5mins with a litre of water and 250g of malt extract.
with the grain, i'd steep it (65-66deg C constant temp) for a little bit in a litre of water and then sparge (with water that is about 75deg C). i know you don't have to do that with crystal grains but it just really seems to be a nice thing to do with darker ales to bring out some of that roast toffee/nut character. i'd just use a stocking leg to sparge my grains cause i'm cheap.
now i don't think that would make a beer quite like oliver and geoff's no 13 but it would be a nice beer nontheless. maybe i'd even add 50g (50g not 500g
this stuff is powerful) of chocolate malt to the crystal grain mix to give it a bit of complex charm.
mmm... that sounds like a nice beer. i think i'll make it now
cheers
-wombat