JD 820 3 cyl desiel?

ok im stumpt,cleaned injectors,all filters,new fuel.problem wont start,me and 2 other farmers have looked at tractor,we can't find the glow plugs? its the last 820 off production line in 1973.it did start up but misfired now nothing like no spark.looked on service manual but no mention of glow plug or plugs.we are dumb founded .can some one help.been in barn since 75 but like to get going .