Putting a breather cap on the early style draft tube would require some creative welding, as the cap on the early breathers clamps around the outside of the standpipe. I'd suggest finding a trashed valve cover, either 6 or V8, and swiping the internal camlock part to weld onto a later model standpipe after removing the top plug.
The bored out freeze plug and grommet approach that's such a dumb idea down at the block would work well to insert a plug-in breather cap at the top of the standpipe. Just weld the freeze plug to the standpipe after cutting the blind plug off.
Jerry
