Here is a link to the spinner filter assembly
here is the tractor supply version
Here is the link to the wolverine heaters. They are sized according to the size of your tank/vehicle. If you have any questions as to the correct size I would recommend calling and speaking with their customer rep. They were very helpful when I originally purchased mine.
I'll try and answer your other questions as best I can, but keep in mind I am no expert by any means. If you take a closer look at my previous photos you will see that the filling bowl and the inlet fitting for the air are both located on the top of the tank. Both are equipped with ball shutoff valves. When I fill the tank with oil, I disconnect the air line and open the ball valve. This allows the oil to drain into the tank more efficiently, and with out the gurgling that would occur if the valve was closed.
With regards to the burner assembly/furnace issues: Since you have used this furnace successfully in the past with propane, I'm going to assume the design is sound.(tuyere placement, plinth block, ect.) If I had to guess, I would say you are on the right track with the air volume in the furnace. Keep in mind that although your blower may be rated at a certain cfm, that is qualified by certain constants that are part of the standard cfm equation. One of these is backpressure, another is the size of the opening you are trying to force the air through. I won't bore you with the equation, mainly because I don't remember it, and I have to google it every time I need to work this kind of thing out. Basically, every blower has limits. When you try to force a large volume of air thru a small opening you encounter resistance. As the opening gets smaller the velocity increases, as does the temperature of the air. This is great for a oil burner because more velocity means better atomization of the oil in the furnace. But..... eventually the fan/blower reaches its full potential so to speak. This means that you can continue to decrease the opening, but the velocity remains the same. This is backpressure, you are essentially exceeding the limits of the blower. Yes the blower is rated at 105cfm, but at what size opening? Also keep in mind that the air needs to get in AND out. You may have a large blower inlet, but if the furnace is relatively sealed and the hole in the top of the furnace is not sized equal or greater to the inlet opening, your not going to be able to reach your full potential with the blower your using. In general I have found that bigger is always better with regards to blowers for oil fired systems. You need a lot of air inside the furnace to get the results you want. You'll notice that larger commercial furnaces (mifco) have two tuyeres entering the furnace just for this reason, even the propane/lp versions.They need two openings in order to get enough air into the furnace to support the amount of fuel they want to pump into it. Try adding another blower, just add a T to your current set up. Borrow a leaf blower from the neighbor, or add a few shop vacs. It doesn't have to be pretty, just get a ton more air into the furnace atmosphere and see what you get. Once you get everything dialed in you can clean it up a bit.
Lastly, be really careful with your fuel line. I would recommend something that will not melt if it came in contact with hot metal. (it looked from your video that your fuel line was some type of plastic/poly, but I may by wrong) Ideally, this would never happen, but when your working with hot metal sometimes things do. I am not the safety police by any means, but trust me when I tell you that this is not a lesson you want to learn the hard way. Also consider a quick disconnect at the fuel tank for the fuel line with the female adapter attached to the tank. In the event of a problem, this would allow you to quickly disconnect the fuel source while it is under pressure, and remove it from the casting area quickly. I am sure you are a well qualified/experienced foundry person, please keep in mind these are only meant as suggestions, and not intended as criticism. My experience has taught me that it is better to plan for the worst when it comes to foundry work. If all goes well, no worries. If everything hits the fan, your prepared, your safe, and after everything cools down you can evaluate and take another crack at it. Just my two cents. Sorry for the long post.