I use a (rubber)sealed outer main bearing with the inner seal removed...
C3 fit denotes the amount of internal clearance in the bearing, not the fit into the housing or to the shaft...Dimensionally a C3 fit bearing has exactly the same O.D and I.D. as a 'standard' fit bearing...
The additional internal clearance, which is only microns, is applied to take account of the high operating temperature and the pressure resulting from the degree of 'fit' between the crankcase bearing housing bore and the O.D of the bearing...
I have used non C3 fit bearings without any problem and I think it most likely that many engines have lost some of the fit into the bearing housings from repeated bearing replacement, particularly if they have been fitted 'cold'...
However, the outer bearing is a readily available (metric) one and can easily be sourced in the C3 fit so you may as well use it on the basis of sticking to the original tolerances as far as possible...Ian
email (option): ian@wright52.plus.com