You started with exactly the right jars... anything with a shoulder makes it impossible to get smoked fish out in the chunks it went in as.
Start with fish that has been frozen as it absorbs the brine more uniformly.
I prefer to leave the skin on, if you prefer it off, wait and do it after smoking.
Cut the fish into pieces as long as the jar minus about 1/2 inch and about 1 1/2-2 inches wide. Try to make them straight-sided. There will be plenty that are tapered enough to make packing easier.
Make a brine of 2 cups non-ionized salt, 3 cups of brown sugar, and 1 gallon of water. I usually boil it with about half the water and add ice after it boils to cool it. Get it as cold as possible. I often put zip-lock bags full of ice in the brine to chill it. I have also put bags of brine in the freezer...
Add the fish to the chilled brine and leave for 90 minutes, NEVER exceed that time regardless the brine or recipe. It will compromise texture. Rinse very quickly in cold water; do not let the fish stand in water after brining, just run it under the faucet quickly.
Place on clean, oiled racks, and let dry until a pellicle forms. It should be shiney and not sticky. A fan will speed things up. Good pellicles do not form in a refrigerator. If it is war out I will some times make a bed of ice covered with a plastic bag to put the racked fish on while the pellicles forms.
Smoke cool for the first bit, raising the temp slowly. I aim for under 100 for the first 30 minutes or so and never exceed 140.
Thinner pieces will be ready for the jars in about an hour. They will be noticeably firm, not hard. They will bend rather than break. It should all be ready in 2 hours, possibly a little less.
Skin it now, if you must. I much prefer to leave it on. In cooking it will mostly disappear except for a little shine.
Pack carefully in the jars to keep from breaking or crushing the pieces. If you have to spice it up, now is the time to put a pepper in on top. I prefer to make it plain and add spices after the fact as it is being used. The fresh pepper added later will taste far better.
If putting it on crackers it is easy to add stuff on top of the fish or in a cream cheese topping.
Pressure cook per your usual plan...
A trick to help get the smoked pieces out of the jar: use an injector with a long needle to squirt a little air under the fish. It will usually slide right out so you can take it apart on a plate.
