Tis all about avoiding eBay for starters! You don't see many genuine engines on there, for the very reason that people are buying blind and with no guarantee.
I have used Sanburn in Coventry in the past (for a PD130 head) and it was in fantastic condition, representative of the mileage and age that I'd been told (25,000 miles) and cost £350 including 4 top notch injectors.
I did try to get a PD150/130 bottom end from them, after my PD115 had a cracked piston. Unfortunately they mucked me around promising parts that didn't materialise, I had to go for a more local alternative...
ASM in Aylesbury supplied a complete new engine - it was a PD130 from a 53 Plate Audi A4 with 27,000 miles on the clock - it cost me £800. Like most breakers yard they provide a 28 day guarantee, so if the engine was knackered they would refund or source an alternative.
It's now been in for 2 weeks and is running sweeeeeet!
Here are the contact details for anybody interested:
ASM - 01296 481788
Sanburn - 02476637376
Cheers,
T