> 1) if we decide to take the view that my SIPP will not be favorably treated in the U.S. could I transfer back to a PPP to avoid the tax issues?
Weird thing to do, because of the time it takes to complete the forms, but yes. I assume, you'll go execution-only, and you'll negotiate out the 3% [?] fees on entry each time or you will pay these too. As a guideline, any assets above 50k are usually better off in a SIP, just on charges, let alone on investment choice.
I can't think at the moment of any 'tax issues' with SIPPs that you would not also hit with a PPP (except foreign grantor trust considerations).
I think when it comes to UK US you need to learn enough to make your own choices, as everybody on this forum has done. I don't think there are any shortcuts which are reliable enough to dispense with the need to research. Not everybody feels they have time, and often they resent it... but there are tax reduction rewards if you get it right (which have generously been given in answers to other topics).