Richard, have a look at the prior thread
http://www.bristolcars.info/forums/8...l-407-8-a.html which has a discussion on the subject including my posting.
When I began restoration of my 411-S1, I bought a "replacement" ABS which ran awful despite paying a great deal of money to tuners to try to get it right. Then I tried bold-on fuel injection; a total waste of money. Finally on the advice of Chris Browne who had gone down the same path, I looked at Holley. Searching the net, I found a firm that prepares custom-rebuilt carbs and bought a Holley 670 avenger. It runs very well. Custom means the fellow in Texas had a long questionnaire that described what it would be powering and for what purposes from which he set the carb up on the bench with the right jets and adjustments. It makes it a bolt-on proposition instead of then paying a performance shop another $150 to put the car on a machine and tune it.
If you do buy this (2010 price was US$250 plus international shipping from Brandon Bates in Waco Texas
Batesperformance@cs.com) make sure to buy the linkage adaptor kit (HLY-20-7 $8.25), the carb spacer (TRD-2084 $19.95) and optionally the dual fuel line adapter (34-150 Fuel Line). Alternatively, you may find the Holley 20-124 Universal Carburetor Installation kit has most of the stuff you may need (I did not go that way, so cannot comment with knowledge, just web browsing).
To see the new-carb specs go to
Holley Performance Products 670 CFM Four Barrel Carburetor.0-80670, but you are better off buying the custom tuned rebuild.
Claude