the stock connection between the push rod and the clevis is 5/16 UNF.
For me I modified at the same time as I transformed the crankset to put in it a universal clutch master cylinder which is easily found.
http://www.talkmorgan.com/ubbthreads.php/ubb/showflat/Number/496823/Searchpage/3/Main/32254/Words/%2Bclutch+%2Bmaster+%2Bcylinder/Search/true/re-clutch-master-cylinder#Post496823
