Can any o e tell me the structural difference between a 1030 and an 1100 ?
I have inherited a 1030 kit and built it as light as possible and would now like to fit a 447 or 503 , in England the wieght is not a problem as our "" SSDR" class has 300 kg . Can any one comment on my plan please . RiP

This is a sound plan.  The main difference between the two is the 1030 is built with a lighter tail.  Not weaker, better engineered. I believe there is also some very minor weight saving in the drag truss of the wing. The 1030 was designed to use the lighter single cylinder engines but I have seen one using a Kawasaki 440.  The 447 or 503 should work fine.

1100 model uses the heavy tail and brace tubes. The seat back is now at station #4,and is no longer a full width seatback, which allows for more leg room and short pull pins for the rear spar attach point . Wing has a lighter(smaller) bottom spar cap. RS-8 instead of  RS-9. Fuselage is 2" narrower. Might be a few more differences that I have forgotten, but basically, the 1030 is the old original miniMAX airframe with streamline cowel, cockpit area and rear decking.
  The original airframe had a lot of 447s mounted to it and some 503s.
I would have no worries about the airframe as long as it was built per plans.
Larry