yeah, the lower link can be a pain, but you are at least going about it with a fair bit more forethought than we did. still, is the tt lower main frame about the same as the xt - as in, fuck all places to maneuver when it comes to placing the lower link? if so, i feel your pain. remember, if it all goes wrong down there, i can at least recommend spring rates to compensate for the leverage discrepancy.
as for the carb, is that an intake off a yamaha quad? if you can adapt some way of allowing the carb to mount into it on an angle, you should be golden. i was looking for one of those to play around with during my build, but came up empty handed. really interested to see how it all comes together for you.
by the way, that's a super nice way of dealing with the front end. takes care of the xt frame having a short headtube, bearing differences, steering stops, AND a place to mount a steering damper all in one pass. mighty nice!