I've got a 1984 NightWatch made by Minnesota Stove Works (Company is defunct now, was around over 120 years prior to '84), and it's an old smoke dragon style insert. The only saving grace it had was a smoke shelf over the flue where some nice secondary burn would occur occasionally. I think where the primary air came in, it traveled along the channels for the firebrick to the back and that's why I would see it now and then back there prior to the mod. I started this about 2 weeks ago where I setup a ladder style air supply and originally had the secondary air coming through the primary draft opening. This was just to see how it did as a proof of concept, and it worked quite well except I didn't have good control over the burn overall. Starting from cold was a bit of a fight, and once it was going it was difficult to throttle back. Basically you had to somewhat babysit it and I'm going to assume it was because of how much the primary draft was affected by my modification. If you'd like to see some pictures of how the secondary air worked in my proof of concept setup, there are some pictures in this thread: https://www.hearth.com/talk/threads/project-old-non-epa-stove-slammer-install-looking-for-advice.103780/ To finalize it, I drilled a 7/8" hole just above and to the side of the primary controls, and used 2 x 7/8" SAE washers to get the required thickness between the pipe fittings. The outside washer and elbow are sealed with furnace cement, and from there it goes into a 45 degree street elbow in the firebox. During this process I realized the left and right side are not symmetrical and it makes sense to me now, many of these units were shipped with non-glass front doors and the air controls were on the doors in that case. You can see where one firebrick is removed from each side, and they just knocked a hole in there and welded a section of flat steel to hold the draft and air plate on. Heck, the air plates themselves are even very different from right to left side, makes me wonder if it was just spare parts to put it together or if they were going for a swirl effect or something. Anyway, the rest of the pipe is 1/2" black pipe and the air holes are 3/32" and 5/32" depending on where they're at. I figure if I've got too many, I can just fill them with a little weld in there but I doubt I've got too few. Spacing of holes are 1" on center, and each section of ladder is 18.5" long, so there's about 54 holes total. I also drilled a few on the back side of the pipe that is facing upwards on the back 2 pipes, these are aimed at the existing smoke shelf to provide some direct air in that area. Once the cement sets up I'll fire this beast up tomorrow and see how it does! I'm kind of anxious to see how it performs with a proper air flow and I'm hoping I'll be able to regulate the burn a little better now. The second week of February I'll be installing a full chimney liner for this as well, currently it's a slammer install and I know that needs to be resolved ASAP. Hoping that I'll be able to get a little more heat from it after that is completed. Eventually this thing will be replaced with a Blaze King Princess Insert, most likely before the next winter season. We'll see how it does with it's new pipes before making a decision.