Since you have the stock off, assemble everything but leave the stock off. Put the long connecting screw to secure the side locks. Make sure this screw only comes flush with the outside of the opposite lock. Do the same with the top tang to trigger plate housing, this screw should be shaped like the surface of the top tang, so make sure you align it so. The rear trigger plate housing screw to end of top tang, make sure that this one also is flush.
Release trip spring for top lever, while holding top lever.
now you can see if things are working correctly. Try selector for each barrel and dry fire each. Notice how far spur lever rides up into recess of top tang.
If triggers work fine this way, then the problem is that the selector slide was binding on the wood. Wood is also removed in this location when installing a HOT in a stock that was a double trigger. So more precious wood has to be removed.
Assemble everything back and make sure those screws are the same way they were without the stock on. Most times if a HOT is working, when dis-assembling I also measure across both side locks with a vernier caliper, and look at the relationship of the rear trigger guard to top tang. The top tang to trigger plate housing could be tight also, but the orientation of the slot should be in line with the length.
Hope this helps, most of the time it is in over-tightening of the screws.