To me it's becoming obvious that the F1 race is becoming more of a popular spectacle than a period race.  I've no problems with replicas being built and used but they should be faithful replicas.  In Classic racing the onus is on the entrant/rider to show that a particular component or combination of components was used within the cut off date.  That leaves us with air cooled motors in xr69 chassis, or 750/1100 slabside based oil cooled GSXRs.  Even then, when the oil cooled engines became available, F1 had already reduced capacity to 750cc so the 1100s are outside the original format anyway.  It appears to me that the rules regarding eligibility are now firmly (loosely?) based on whether the bikes look pretty, go fast enough to push the speeds close to TT speeds, or are deemed interesting enough to get some publicity.  The race needs variety in it, but that variety should be limited to the machinery available and raced during the period.