Are MC18 head and cylinder designations similar to MC21? I am familiar with MC21 head and cylinder designations but my MC18 top end has me baffled. Head says KV3R E-1. I do not understand what the R means. I would expect it to be H (for R spec) or L (for SE/SP spec).

Cylinder is stamped "L" on base opposite exhaust and on right side where i would expect to see A, B or C. Cylinder base is also stamped F with a circle around it. This I thought would be H1, H2, H3 (for R spec) or L1, L2, L3 (for SE/SP spec)?

Thanks.
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MC21R9N track
MC18R2J track
CBR954
CR250