This is the problem I found when looking for a UK engine shop to do my SB569A crank swap, late 2007.
There was not one UK engine shop on which I could find anything like uniform good reports.
In one or two cases, people were happy with the job but only after they went there, months after it was supposed to be ready, and kicked somebody's butt. And then kept repeating the exercise over and over.
I sent the engine to the USA. The engine shops out there are much more experienced and it is much easier to due due diligence. I used
Barrett Precision in Tulsa, Oklahoma. The whole job cost $12k including the $2k crank, engine rebuilt to NEW (not overhaul) limits, plus shipping, and this was way less than I was quoted by UK firms. I visited them too, when the engine was in bits, and wrote it up afterwards for anybody who is interested.
The one thing I would do differently next time, however, is to use a courier (say DHL) to ship the engine there and back. This costs about £3k (total) but avoids problems which one occassionally gets with air freight companies which are generally staffed by ... shall we say .... not the sharpest people. The monkey air freight cowboy outfit I used "lost" my engine for 4 weeks.