I have an engine which came in pieces which was converted by Richard Hutchings.
It was a blown ulster conversion 10 stud block on magneto crankcase.where the extra studs tap into the block bosses had been welded inside the c/c.The front and rear of the 8 stud hole pattern needed to be blanked off,sorry no photo's.
The welding for the s/c mounts and these extra top studs distorted the c/c so wouldn't try this way.
I don't believe the 10 stud block idea on an 8 stud crankcase is a very good one,the next problem being,in my case,one of the "new" stud holes happens to be tapped into the front camshaft oil gallery so its got 60 psi behind it and have spent a lot of time trying to seal it insitu.
Robin Jackson I think post war fitted blocks or angle brackets to the tappet chest side of the block to hold it down,The strongest part of the crankcase.