This arrangement allows you to use the older style of forks used by Triumph and BSA (the latter with some modification to the bearings) and they are handsome, elegant forks that work well when set-up properly. However, having opted for OIF cycle parts I'm now faced with a small obstacle, in that the OIF steering stem is of a considerably smaller diameter than the pre-OIF one.
There is an excellent write-up that illustrates precisely this scenario here.
I prefer the tapered roller bearings to the original ball & race type. There are conversion kits to fit tapered rollers to the pre-OIF Triumphs and BSAs, a sensible upgrade for any motorcycle in my opinion. In this particular case though, I could do two things:
1) choose one of those conversion kits and machine some inner spacers to slide on the OIF stem, thereby increasing the diameter of the stem to that of a 1970 stem; or
2) machine a "cup" type spacer to fit in the steering head and accept the original OIF bearings. As explained in the Chopcult article, this is not advisable and there are some practical reasons why this is so.
SRM, make a bearing kit for this very purpose but it won't fit the Triumph neck. Again, great for a BSA though!
In the end I found a tapered roller bearing conversion kit for Triumphs up to 1970 from Supreme Motorcycles and will machine a set of spacers to adapt it onto the OIF stem. I think that's the most straightforward thing to do.
Finally, here's a very useful how to by Lowbrow: http://www.lowbrowcustoms.com/index.php?l=page_view&p=tech_triumph_tapered_roller_bearing_coversion