1968 340 Cam Choice (Again)

go to the 318 cam thread stickie and you can see the stock cam and others with similar durations and choices of LCA's
that said true compression would help
you need to determine if you CAN close the intake earlier by shortening the duration or closing up the lobe centers
Then know that the very extra long closing ramps (for that duration) can be shortened allowing the exhaust to close earlier and close up the lca that way
as yr said the factory cam is a compromise based on warranty and the the factory valve springs
depending on how much work you want to do you can lighten up your springs with beehives and their lighter retainers
if donig the heads you can use lighter chevy valves
etc
The 268 comp is no better than the stockcam except that it is ground with a SLIGHTLY narrower lca
There are better choices than either
but the stock cam will work if your compression is what you say it is
it is a dog with less (that's IMHO of course)