Hi, sorry I wont be able to join you, as Ive just returned from a six-month trip from Europe to Australia - and that was bloody great, by the way!!!
Will you have a carnet for your Enfield, if you decide you will head towards Europe? Pakistan will require it, and so does Iran, even though they might not be as absolute about it as the Pakistanis. I believe you will have to be able to cross into Pakistan, no matter which route west you will be taking after that.
And about getting into Thailand, surely you are aware that you wont be able to go to Burma on your bike? Which means, from India you will have to either go to Pakistan, then China then Laos then Thailand (not very simple, a loooooooong way, and China will require heavy preparations+cash), or you will have to ship the bike to Thailand or Malaysia.
If I was heading from India to Thailand, I would consider flying first to Bangkok, and buying a bike from there. Might save you a large hassle that is shipping out of India, and find a much larger selection of bikes in Bangkok, too... nothing against the Enfields at all, but they do require a certain level of mechanical skill. In India they can be fixed anywhere, but in other countries you must be able to do pretty much everything yourself.