I'll second those who say that each car has its own sweet spot as far as
timing goes. In the UK, and many US drivers do it as well, there's a 'road
timing' method that works quite well. It involves loosening the distributor
just enough that you can turn it, and driving the car a bit. It's kind of
long and involved, requires some practise, but it's fun and usually results,
if done right, in a superior timing for the individual car.
I disconnected the vaccuum advance on Rags, completely. I was advised that
the advance was between 3 and 6 degrees, not enough to make that much
difference. I haven't noticed any lack of power at high RPM's, nor at high
speeds. I would worry about the centrifugal advance springs, as I think they
do make a difference.
The engine is sort of a lump, stock. Of course, it's overall a very reliable
lump (electrics excepted, and that little problem between #2 and #3, of
course) But it's a workable lump, and one that can be tuned very nicely, as
has been pointed out by several list members. Don't despair of making
modifications to it with the expectation of meagre results. The tuning books
for the MG are very helpful in this regard, and I'd recommend one if you're
going to make modifications to your engine.
75 MGB 'Rags'