Made a retainer I'm happy with, seems strong enough, just need to clone it for the other side then it will mount using the socket holes in the conventional way. I probably wont use any springs to keep it neater, just clamp it down slowly in a balanced fashion until I'm happy it's stable, level and has sufficient core pressure.
As this block is at least 50% about "image" here are some pics of the finished "shaped" retainer fitted to the small webbed section I left in two opposite "V" parts of the block base.
