Boiler <-> Flue connection issues

First off thank you for any assistance, I inherited this wood boiler setup upon moving to Idaho and my goal is to get it solid and reliable and eliminate the finicky issues and smoke-out.
I have a wood fired boiler with about 15 2" x three feet long fire tubes before the smoke exhausts out the stack. The fire box is approximately 30 gallons in size. The boiler has a constant draft fan supplying air. The air pushes past a damper that has an attached weight that closes when the fan shuts off.
The boiler has a straight 8" single pipe coming out the back of the unit. There was a 30 degree bend selkirk metalbestos pipe simply slid onto the top of this pipe. The flue continued about 9 vertical feet of connected metalbestos pipe out the roof. Some of the seams were taped but I noticed two 30 degree sections upon disassembly have deteriorated and need replacing.
My first problem is that if the fire got too hot, adding a couple pine logs or too much larch bark or too much wood in general, the damper prior to the firebox would start flapping wildly and the seams of the flue pipe would smoke out the attic. This leads to my second problem that I can't fill the fire box as much as I'd like so I end up feeding it once an hour or so and this will gain about ten degrees water temp on the boiler per hour.
I'm figuring I need a 258240 adapter to properly connect the boiler to the selkirk pipe. I'm also intending to replace the corroding 30's and seal every joint with silicone and tape as I work my way back up the chimney. I was concerned that I would need a positive pressure pipe such as ICC Vip+ but upon contacting ICC they said their pipe is not certified for solid fuel. Upon further research I became optimistic that simply reassembling new pipe with the proper adapter would be a permanent solution.
So this is my first experience with a boiler and flue pipe and I would very much appreciate any feedback if my plan is solid or if I'm overlooking anything and I will need to run on propane backup all winter(not ideal). The Selkirk does not list positive pressure and that was my main concern although I don't think I'm dealing with much pressure at all.
Thanks a bunch

The boiler was manufactured by a company in Sandpoint called Swhift. They no longer do boilers, only stainless fabrication. I have a 2 inch forstner drill bit attached to quick connect rod extensions that I use to clean the tubes. I can climb in the fire box no problem with room to work the drill and bits. I have found creosote buildup to be pretty minimal and I think the fan contributes to a pretty complete burn.
The pictures don't show the complete fire box as it's still full of wood from last year's final fire. It is a cylindrical chamber with a cone shaped bottom. The air is blown through a tube going straight down the front of the box to the bottom of the cone and also from the two outlets in the right of the picture of the fire box.
I added a 4 foot section of pipe to the top of the chimney when we moved in thinking it might help with the smoke that comes out the load door when I add wood. It still smokes into the room when feeding the boiler. I was under the possibly mistaken impression that because the unit has a fan feeding combustion air that the draft was not as important on the back end.
So the puffing is a result of lack of combustion air, good to know.
I was not aware of fire brick and I'm not sure what the best placement would be if it would help. I'm pretty sure the entire burn box is surrounded by water so would I layer the bottom cone and a little up the walls or would that effect heat transfer to the water?
I also just want to be sure that the selkirk pipe I'm working with is correct for my application. On reflection it doesn't seem like the system could be under hardly any pressure, the fan is pretty tepid, I had originally thought it was because of the puffing and smoking.
thanks