Grizz 44,
An intake like the K&N or MAC do not add horsepower, they free it up. Since most OE intake systems are geared towards noise reduction, an aftermarket intake is louder and allows air to enter the engine with less restriction, the gains are there. Do not expect an intake to make it a Mustang. You will gain a maximum of 5 to 10 HP. Not much considering the Trac weighs at over 2 ton.
I have a K&N. K&N is a well respected name in the industry. The price is higher but, IMO, worth every penny. If I were buying a filter today, I would seriously check out the Volant intake.
As for shocks. I am running Monroe Reflex shocks. I am satisfied with them. Bilstein makes a darn nice shock. They are very high quality. I installed Bilstein shocks on our 34' Class A motorhome and the ride is awesome. I don't know much about the Rancho shocks you mentioned, but Rancho does also make a nice shock. Either way you go, you will be more then happy with them.
Tom