Coil - Which way round?

[alanworland]

My sidevalve has a later Morris coil fitted (LA12 45053E dated 8/55) and since converting to negative earth it seems logical to reverse the coil connections as the terminal marked CB (originally going to the contact breaker and hence earth and + Positive) is now negative?
After doing some admitedly crude tests I have found that I can get the spark to jump about 11mm with the coil connected either way round but there is a 'fatter' short spark with the coil connected so the CB terminal is to the contact breaker.
Surely this doesn't make sense as the original installation was with the coil CB terminal going to positive through the distributor, as designed - it now goes to negative through the distributor, but gives a better (it seems) spark?
All Minors were positive earth were they not?

[bmcecosse]

The CB should certainly go to -ve. But - if it's working well the other way round - leave it be!