Ok.. so your tractor is 6v p-ground, and your kit is the one for 6v pground. is this a pertronix ignigtor or igniterII kit?.. or a hobby low-current breaker-switch kit?
In any case.. those 6v e-kits are finicky on power.. voltage rather.. anything under 4.5v and the logic won't work. thus you must ensure your 6v system is in top shape. I'd go for a new battery, and check your gen / vreg. IE.. install new wires and clean all connections and grounds.. bat ground to fram.. and cable ends.. make sure gen charges good.. etc... check grounds at vreg.. clean up connections there too.
if starter drags... you will have problems... make sure you have the big 1/0 thick as yer thumb 6v cables.. not wimpy 4ga automotive 12v cables.. they are the prime reason for dragging starters.
that 172ci engine is a bit to turn over.. so give it all the help you can.
soundguy