Hi,
The extra nipple on the exhaust is a preasure outlet to preasurize the tank. OOPs Isee now there are two, I would reomve one and peplace it with a smallsame thread bolt with a bit of locktight to secure it. I did notice missing bolts on the motor install. That is not a good idea, you need four to dispurse the load to the lugs evenly.
Do check for proper side and downthrust if required by your plane's instructions. Good luck.