There are very few places that can rebuild
reliably. Unless you you are near one it's out of the question IMHO. A home garage minor rebuild
of a 4 to 8k hour engine
will usually buy you 4k hours. 3 to $500. Hone cylinders, new rings, valve job, thermostat, hoses, belts, all gaskets, glow plugs, injector rebuild, water pump
pump rebuild, and anything else that looks bad. Don't take the head
to a machine shop for surfacing. Just clean valves and regrind seats and new valve seals
. Machine shops ruin a lot of otherwise good heads.