I would figure 2.5-3 hours on the loin. Pulling at 145 is a good temp. I usually pull at 140 and let it rest to get to 145. What are you stuffing the loin with that will have some effect on how long it will take. If you have a cooler ready and wrap it in foil this will hold fairly well, but don't let is sit too long or it will dry out.
I think most people here that do racks of lamb, do them over high heat, just because there is very little fat in the meat of the rack. Depending on how you like your lamb, if you pull at 130 and let it rest you will have carry over heat that will continue to cook the rack and push it to 135. I think that is medium for lamb. If you want it rarer you will have to pull earlier.
Both of these cuts are very lean and will cook fast once they get up to 100. That is when you need to watch them.
The question I forgot to ask is what are you cooking on?
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