i suggest you use a caliper and actually check the port. but triumph is probably more organzed than norton.
i had this problem when i bought my norton commando engine. it was the last of the 750's so it was a RH6 stamped commando head meaning it had 32mm ports just like the 850 even though it was a 750. It has a higher compression and the first units were called combat 750's. mine is the latter made which don't have the main bearings problem.