+1 on what Lethal D said, it looks lush.
Don’t know specifics about the seat tube or ISCG mounts, can’t seem to find any info on tinterweb.
Buy yourself some of these to measure the seat post diameter
http://www.ebay.co.uk/itm/150-mm-6-Digital-CALIPER-VERNIER-GAUGE-MICROMETER-9717-/170701667282?pt=UK_Measuring_Tools_Levels&hash=item27be9cbbd2
Digital calipers are really useful for things like bolts, shock mounts and figuring out the size of bits and bobs if you can’t find the manufacturers specs.
ISCG mount thing you link to should provide you with the mounting points you require and possibly give you a better selection of chain guides to choose from. Although I believe you can get chain guides that mount to the BB in place of a spacer, just like the adapter. It may be easier to get a specific chain guide rather than an adapter then a guide.
It may be worth having a look at the Trek forum over on MTBR and asking there if you have no luck here.