I recently received an NECG peep sight for a weaver base to try. It's a nicely made site and would almost work. I would have to raise the front sights a little more (~1/16"+) to compensate. Unfortunately, my barrel shoots quite a ways out of windage center. It shoots accurately, just off center too much out of adjustment. There was not enough windage adjustment in the NECG to compensate.
NECG peep sight
http://www.newenglandcustomgun.com/images/Weaver-Peep.jpgI picked up a Williams WGRS sight for my Encore and have been doing some estimations with my TCR barrel. Assuming a thin flat base, It would require even more height out of the front sight to compensate, than the NECG, but seems to have enough windage adjustment for my needs. Mounting it on the TCR monoblock would be difficult. Unfortunately it would have to be mounted right against the monoblock. A weaver base would add even more height (too much).
I think I may have found a custom solution. I am going to order one of these "PeepRib Muzzleloader Peep Sight" and have a friend machine the bottom flat (to the thickness of a weaver base), trim the length and drill/countersink for mounting to the monobock.
PeepRib Muzzleloader Peep Sight
http://www.eabco.com/Muzzleloader03.htmI have also ordered a couple of front sight options to raise it another .075" or .250". Between the two something should work.