Those Landcruisers are kinda tight for muffler space and room over the rear diff, so you really ought to run a collector and single muffler and outlet pipe. A 2 1/4" or 2 1/2" collector-to-outlet should be great, with probably 2" from the headers to the collector. Those tubes can be as short as you want or can extend almost to the muffler. It's not a critical dimension for a setup like you've got.
Tell them to use the aluminized pipe if they have it instead of just the plain steel w/ zinc coating. It lasts a lot longer and looks better.
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David
newbie #4153