I'm considering an LS swap, the ideal engine candidate being the 5.3 liter L33, on my 2003 Disco. Is it worthwhile to accompany the engine upgrade with a custom exhaust upgrade?

For background, the only performance upgrades I want to include as a part of the swap are focused on letting the engine breathe better (i.e. better intake, headers, exhaust). When I checked the diameter of the exhaust systems from Magnaflow for the 4.6 LR engine is 2.5 inches and the for the 5.3 GM L33 (swap candidate) is 3 inches. I'm trying to avoid having the exhaust being the choke point in the whole system.

 

you will have to have a custom exhaust to some degree, but why re-use any of the stock system?......have a high flow stainless exhaust made....

 

Stock manifolds (that fit) will be fine for your goals. I am running a 5.3 with stock truck manifolds into dual 2.5" pipes. With an LS1 top end, mild cam, and custom tune I'm making plenty of power, @325 HP or more. The 4.8, 5.3 and 6.0 trucks have the best iron manifolds.