1600 valve guides

[lancialulu]

I am in process of sorting a 1600 head out with the ubiquitous thread problems of cam cap retaining bolts, and I have found the valve guides are non standard (apart from one?!). It seems they have a ribbing inside at the top portion (see photo). I have never seen this type before. It was gasflowed and used for racing so are these guides (used for both inlet and exhaust) better for hot racing conditions or what. Needless to say no valve stem seal was present on inlets (I wasnt expecting them on the exhausts), and none could be fitted as there is no shoulder.

Any thoughts?

Tim