I haven't checked in here lately, but I saw this thread and thought this might help. Here are the instructions directly off of the T/C Hunter tang peep sight:
No. 7194 Hunting Style Tang Mount Peep Sight
For T/C Hawken, Renegade, Big Boar, White Mtn. Carbine,
and Pennsylvania Hunter
WARNING - Never attempt to install a sight on a loaded firearm.
Always ensure that the firearm is UNPRIMED AND UNCHARGED.
Failure to heed this warning could result in an accidental discharge
causing injury and/or death to the shooter or bystanders and
damage to property.
Read the instructions included in this package before attempting
to install or use this sight.
Installation of the T/C Tang Peep Sight on Thompson/Center's
Traditional Cap Lock or Flint Lock Muzzleloaders:
Hunting style Tang Peep Sights require the drilling of either
one or two additional holes in the tang for mounting.
For the White Mountain Carbine and Pennsylvania Hunter models,
two additional holes must be drilled and tapped.
Place the sight midway between the front and rear tang screws,
then center the sight side to side on the tang.
Use a prick punch to mark the front hole only. Use a #29 drill
and an 8-32 tap to thread the hole after it has been drilled.
Once the front screw has been secured, then mark the rear
screw hole; drill and tap.
For other traditional T/C side locks, it will only be necessary
to drill and tap the front hole. The back hole uses the
existing rear tang screw found in the rifle. Once secured
with the rear tang screw (and aligned side to side on the tang),
mark the front screw location with a prick punch - use a #29 drill
to drill the hole, and a 8-32 thread tap.
If you have any questions on this, call the Thompson/Center
Service Dept. at (603) 332-2333.