Your engine temps sound to be fine although "too hot to hold your hand on for any length of time" is a bit vague . I'm in the process of running in an iron piston engine in a similar manner to what you've been doing. I gave it an hour running at between 6-7000 revs so a very rich 4 stroke with all castor fuel. Surprisingly the temp actually came down considerably during that hour as it ran in but this particular engine had an extremely tight "ABC type" pinch which slowly loosened. Head temp dropped from 146F to 115F at 7000 revs after an hour and then stabilised. So your "barely warm" is fine. I've now got to the stage where I'm taking it to the 4-2 break point to start building up some heat in the piston and this happens at 11,900 revs (with an 11x4 prop) where the head temp is 200F which gets uncomfortable to the hand very quickly . So your "very hot" sounds about right.

As for the change in tune when restarting, it could be a slight air leak from the needle valve (use a piece of fuel tubing to seal it) or possibly that it can't quite make up its mind if it wants to 2 stroke or 4 stroke so picks one or the other.