I would not order new bars until you get the actual TW. Internet says that's a 35' trailer with 9990 GVWR. Tongue weight is typically in the 12-13 percent range and sometimes closer to 15 percent (like us). The actual TW could conceivably be as high as 1400 or so lbs depending on what's loaded into it and what options/upgrades/mods it has. You don't want to find that 1200 lbs are too small. You could conceivably even be over the receiver rating.
Reese has a chart somewhere showing how to size spring bars based on actual TW. I can't find it at the moment - maybe it's not around anymore.
Our TT has a dry TW of 540 lbs. When we ordered the TT, I ordered 800 lb trunnion bars in advance thinking that 800 lbs would be more than adequate. Could not get enough weight transferred to the steer axle even after going to a scale to play with the adjustments. The scale showed the actual TW to be over 900 lbs. Ended up having to order 1200 lb bars and then it was fine. Reduced bounce in the tail of the trailer quite a bit too.
With tongue weights around 1200 lbs and up, you can sometimes have trouble with the Reese forming screws holding the cam arm brackets to the A-frame. The snap-up brackets can also be a problem. Reese has a heavy duty snap-up bracket and as well, you can use forming screws to help hold it in place. If you find the forming screws are not staying put, there are ways to better secure the brackets in place. There's also a couple of other things to know about the Reese DC setup when TW is on the higher side.
Then there is the question of whether or not the F150 is adequate for the GVW and TW of that trailer... Personally, I would not tow that large a TT with a 1/2 ton truck.