I have a 93 w250 club cab. 4"front 2" rear lift and I am curious to know can I fit 35x12.50r20's under there? Also what's the largest - offset rims I could fit there? Thanks boys

 

35s on a 1st gen with 4 inches of lift will usually work if you keep the rim width to 8 inches or less. There might be some rubbing when turning and hitting a bump at the same time.
The offset needs to be about stock or the front tires will rub badly on the rear of the fenders.

If you OK with cutting the fenders, you can go wider on the rims

 

I wanted some 20x9 with -24 mm offset. Pretty sure that'd work. Correct me if I'm wrong

 

9 inch rims is getting a little wide for 4 inches and not cutting the wheel wells.
I have never owned 20 inch rims, but I have lifted many an old Dodge over the years.
I have run 33s, 35s, 37s, 38.5 on '72-'93 Dodge trucks with no lift to as high as 7 inch front and back lift on my old '72 Powerwagon.
The '72 had cut out front fenders and heavily modified inner wheel well.

 

Fwiw I run 305/70/16 on a 10" rim with only 2.5" over stock springs in the front and stock everything in the rear, never had a rub after I replaced the sagged original springs.