I have one of those W/R single shots with the tang safety, originally a .303, a little like a Pacific Ballard with a full length cleaning rod under the barrel. Maybe twenty years back had it rebarreled to .30-40 with a new forend. That action is one of the most desirable of the Farquharson-style variants, much more so in my opinion than the second quality 1897 W/R where the safety is on the trigger guard. That you are thinking of taking off the tang safety and making holes in the action for a tang sight fills me with horror. 1878 has the solution, using the CPA extension bar.