I downloaded some part dimensioned drawings ages ago to make one but too lazy/stubborn  to find them so going for it by gut!   Some 32mm round bar last seen on the core drill guide when replacing the water main. A ropey old bit of 1/4" angle last used umpteen years ago for welding practice. A Starrett etc.         After a half ar$ed attempt at removing the mill scale:     Don't wait up...