new need some help

hi guys i am new a new and need some help
I had been thinking of lifting my old ford f150 up and turning it into a offroad truck. Well a friend had a 85 chevy already lifted with 33 inch tires.
He said he would trade me for the ford he wanted a short bed stick and the chevy was a long bed auto. plus it needs some work more then what he let be known but so be it.
I changed the back breaks and wheel cyclenders. i dropped it off at the local shop to have the rear axle filled with oil.
The guy told me the truck was unsave to drive because it has alum. blocks in the front when it should have leaf springs.
The truck has a 4 inch susp. lift with a 3 inch body lift.
He told me he could change the blocks out for leaf springs for 500 bucks.
But i had been thinking about going up to a 6 inch susp. lift to clear bigger tires. he wants 1700 for a 6 inch lift. From what i have found online i can get a 6 inch lift kit with quad shocks and back leaf springs for 1000 or so if i do it myself. rough country also says it takes 6 to 8 hours to install. so at 55 an hour that should be about 450 bucks for labor. so i am not sure where the other 250 is going for one.

So i am thinking of doing the lift myself with some help from my dad
if i go with a 6 inch lift staying with the 3 inch body lift how big of tires can i go.
also when going with bigger tires do i need to look at any other factors when determining which i buy.