Which would be a better base for a towing/off-road/beach 4x4? Thinking older chassis say 98-2004ish?

Already have a Chev 6.5L Diesel motor that would go into the car....OR would you tune up the 4.2L Turbo diesels they come with?

Do either have any inherent chassis, suspension, driveline problems?

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K.E.R.S!!!1