A philosophical moment ...
Thanks to all that have responded so far ... and please do not let this post stop further ideas coming. All are helpful - even if outlandish they can spur a creative moment.
Firstly, after my initial realisation of the cock up I made (something that is not unusual in my spatially challenged life), my frustration remained mainly for the precious time it would use to make the repair. Repairs do not phase me that much. I think that they are part of woodworking and life. Evaluate, plan, do. This is an opportunity to do something interesting, to be creative. I want to be reminded one day of a success, not of a failure.
It strikes me that few are willing to start again. Cut out the dog hole strip and re-make it. Perhaps there is a simple fix, and I appear determined to do it the long and hard way, but modifications as repairs are rarely satisfying. Far better to have the Real Thing.
Reshaping the dogholes is not practical. It is not just that they slope at 2 degees on both sides of the shaft, but that the head of the dog faces the wrong direction. Even if you turn this around, the support for the dog hole head is now absent. I don't want patches.
In the repair I plan the dog hole strip only gets removed as far as the last dog hole. There is no need to touch the side board or the area for the tail vise, and the latter includes leaving the dovetail well alone.
The tool of choice is a power router with a fence running along the outside edge of the bench. I have a 1/2" bit to run in a large Elu router, and plan to take very shallow cuts (although I find the Oak so easy to work after Jarrah).
The advantage of a router is that I can create a perfectly vertical, smooth and parallel set of grooves. I can work the top first, which is the show side, to a depth of 2". Then flip the top over (flip is a relative term for something that weighs 100 Kg!), and make the identical cuts on the other side. I will work short lengths once I get to the underside, clamping each section carefully to prevent any movement of the top. This is not to avoid binding, as with a saw blade, but the inadvertant routing into the sides of the dog strip, which will affect its parallelism.
The alternative is to rout the top section, as described, and then use a hand panel saw to remove the remainder of the waste, with the sidewalls now able to act as a guide for the blade. Your thoughts on this are welcomed.
I have managed to order another length of Oak. This means that there is a good chance that the repair will leave the bench top better than before! The existing dog hole strip is made up of several joined sections. Now I can replace it with one long, continuous piece. An ill wind and all that ..
Regards from Perth
Derek