I replaced the stock retracts with Robart Mechanicals in my WM P-51. The strut is a bit thicker than Hobbico. I use then on an 11lb plane and work fine. Also "glass the inside area of the mounting blocks. I cannot tell you how many times I have seen retracts pull out or go through the wing on simple landings. I have been flying mine since June and no problems.
I also run a St G.90 with a 12/10 apc prop. It can handle it. If your uncomfortable, throw a 61proor fx in it. I mount my .90 sideways. I have to remove the head to get the cowl off.