I put a 5.0L in my 88 STX 4x4, completely different Truck.
I got the complete adapter Kit including headers, Oil Pan, Oil filter Relocation Adapters, from L&L Products. A little pricey BUT I have to say they were very impressive, the parts were made of heavy gauge steel, the machining was top of the line, the headers were made from heavy gauge steel w/ ½” flanges, all of the parts were HD all the way; “You get what you pay for”.
I contacted then about a kit for my 2003 and they do not have one but IF they did I would buy it.
4x4, 5sp, Std Cab, Stepside, E4 Red
4” Lift - Coil-Overs, 6” SkyJacker Leafs - No Blocks (Mistake)
31 Spline FX4 Rear Axle, 4.56s and OX Locker, Hurst Shifter w/Optional Stick and "Made by Grev" alignment adapter