RE: Open or shielded bearings for a DA 85???
To answer the question in post one, Yes you can use a open bearing on the inside and a one sided sealed bearing on the outside but you will lose performance.
The only reason most high performance RC engines have two sided sealed bearing is to help stuff the crankcase.
Fox Gas engines still use open bearings on the inside and one sided sealed bearing on the outside and most Sack's Dolmar type engines also.
Milton