A picture would help identify it. A customer could have it vented any way he wanted since many were sold through factory showrooms right in the same building as the fabrication shop. Since they were more efficient with rear or side vent, it would be advisable to put some type of baffle plate across the top vent opening.
At a minimum, you should have a damper in the first piece of pipe.
Any high temp grease is fine. I like silver anti-seize too since it's higher temp and seems to last. Keep the threads greased through the hole in the door behind draft cap too. You don't want too much wear on the threads in the draft cap.
Here's an oddity where two Papa Bear stoves were ordered with 8 inch outlets. All single door stoves normally had 6 inch.
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All the sales people I met at the PA Factory Showroom were trained well. Most did installs, managed or owned the business. So you had to prove to them you had an exceptional case that required something fabricated special to work better in your installation. One reason for needing a top vent would be in a small building that floor space is limited. The pipe out the back requires the stove to take up more room for clearance to the wall than coming out the top of stove.