In case it might help, happy to share some perspective. My first Bristol was a Britannia from Bristol Cars in the late 90s and I drove it for a bit less than a year before asking the factory to upgrade it to Brigand spec to get a bit more urge. The conversion was pricey but worth it when it worked. (new bonnet, different engine mounts, exhaust, etc). Unfortunately I didn't have the opportunity to use the car regularly, and it would go out of tune - probably for the reasons that Thor elegantly describes with the priority valve. (If only I had known at the time..) It was a wonderful car when Eddie at the factory had breathed on it, but the logistics around keeping it in good fettle while living in a different country and only using it occasionally led to it's sale. With the benefit of perfect hindsight I should have put in the injected 360 and 4-speed instead of going the turbo route. I drove a Blenheim during a factory visit and felt the performance to be equivalent (and a bit more linear) and would recommend looking at them too.
Never loved the non-matching modern turbo boost gauge and iirc swapped the location with the voltmeter so it wasn't glaringly in the middle of the instrument nacelle.
That drainpipe exhaust made a lovely burble though, and who could resist the bonnet bulge and quad headlamps.. Liked that car a lot (as does OPEC). Happy it went to a good home.
https://www.flickr.com/photos/107289...57637155693923