Doing the exhaust on my 99 ford f150 xlt 5.4 triton v8 4x4 8in lift 40in tires?

I'm going with the magna flow performance true dual 3in outlet, but want to run 45% elbows with MBRP 5in inlet and 8in outlet tips to come out after the rear tires at an angle. How could I get the 3in to an 5in and would it even sound good?

No, it won't sound "good". In fact, that's a really dumb idea, and might even get you busted for noise pollution.