The 1983 Ford 300cid 4.9 litre inline 6 had 120 Horsepower at 3200 RPM and 250 foot pounds of torque at 1600 RPM.
The impressive nature of this engine, besides its durabilty, is how low in the RPM range peak HP and, in particular, peak torque are made.
Some argue that the replacement of the 4.9 in 1997 by the 4.6 litre V8 is all good news but in reality the 1997 4.6 didn't reach its peak torque of 265 foot pounds until 4000 RPM! That being said the 4.6 V8 breaths much better and revs much higher which translates to more HP and better fuel economy.
Still the 4.9 is an incredible engine that deserves its place as "the best engine Ford ever produced".
Could be that its just a defective rocker arm... either if its the original it could be damaged, or if its new, just defective
that is the transmission return cooler line