Use an installer to install, plenty of oil.
Seven-sixteeths -20 threads per inch, if by chance the orig threading fails, you can go and use a coiled thread insert, as in Heli-coil. Worked for me.
A suggestion, before installing the balancer, slide onan O-ring to go between the balancer and sprocket, this will cut down on oil seeping by the interface between the two, Chrysler does it.
I might need an education here, but I thought 68 was the last year of 327 CID, after that it was 307 & 350