Only you can decide whether spending more money is throwing good after bad, but I think if it was me I'd try one more round of fixes ...
I'd be very cautious of jusdging a place by its hourly rate, especially going somewhere based on a low rate. The country garage I used to go to charged 35 GBP + Vat per hour & were reasonably competant but nothing special, but the next time I went it had changed ownership & mechanics and the price had gone up to 49 GBP + VAT /hour - might as well have burnt the money as they were such bungle***** the work had to be repeated elsewhere. 2nd country garage (now folded) in same village, same hourly rate and used to be competant, but the older mechanics retired & they got a total prat in reception who thought he knew better and your car wouldn't get exactly the work that you'd specified done, often this wouldn't fix the problem.
The place I go now charges 95 GBP + Vat an hour which sounds horrific, but they only charge half the hours I'd expect to be needed to get the job done. I've recommended them to friends/family, some with exotica & classics & they've always been willing to take difficult/fiddly jobs on.
Sadly they're in south cambs so no help to you at all
Yes it does sound like timing chain issues from what I've read. From what I've seen it needs specialist locking kit & experience, hope someone can give you a recommendation