I've installed three sets of wide-spaced double set triggers from the old Ballard rifle company when they were still available.  The parts came hardened and they were a fairly easy drop-in.  The only thing that may give you problems would be the knock-off spring. It might be a little bit too long at the tip and you might have to work it down. Right now I think the only company making wide-spaced double set triggers is MVA and if their parts are as good as the Ballard, which I think they are,they should be easy to install. Ask them if they need hardening. You will need their lower tang, lever, and you'll also need the long-tail sear and a fly installed in the hammer. You may also check with Wyoming Armory to see if they're making the parts.  I've also put in two sets of single set triggers and their pain in the butt but it can be done. The biggest problem is that the knockoff spring has to have just the right curve so that it does not put too much pressure on the knock-off, otherwise the sear will not drop into the sear notch. If it doesn't have enough pressure then it will not knock the sear out of the sear notch.  Those issues can also cause problems with the half-cock notch. The triggers will work in a coil spring action as well as a leaf spring action.  There's no difference in the parts. If you have a coil spring action, check the hammer, it may already have the fly installed

Thanks guys
Mike

Would the single set trigger use the same lever and lower tang as the standard rifle?
Thanks Mike

3 lower tangs. #1 tang single trigger and single set are the same. #2 close couple is one. then #3 is the double set trigger tang. I have seen the single trigger tang modified to take the close couple  triggers. Ken

Give Steve Baldwin a call at Mechanical Accuracy. He used to install a fly in your hammer for around $50 if you supplied the fly and the pin. I don't think one could be installed easily without having a jig to hold the hammer and know exactly where to drill the hole for the pin and cut the slot for the fly.  The rest of the parts involved are reasonable in price.  You will need a trigger with adjustment screw, a fly, a fly pin, a trigger catch, a knockoff spring and a little tiny spring set in the trigger to put pressure on the catch hook.