Perkins has a strong history of solid performance and 6000 hours is not much more than 50% service life between overhauls even for a pessimistic outlook. Caterpillar used quite a few Perkins diesels in their small generators and their reputation is sound.
We do not necessarily like the MeccAlte heads, but mostly a matter of ready supplies and personal preference, not any performance related issues I am aware of.
I would take a fairly careful look at water pump, belts and hoses at this hour count. Are the exhaust ports clean and uniform? Does it start easily with minimal cranking? Clean filters? Clean lube oil? Priced right?
dieselgman