Part Description = HEAD ASSEMBLY, CYLINDER. Model Count = 4. GS550B 1977 549 GS550 STREET. GS550C 1978 549 GS550 STREET. GS550EC 1978 549 GS550E STREET. GS550N 1979 549 GS550 STREET. Hi/AK/PR/APO AP may be higher. Customer service is our #1 priority. We strive to be the best at what we do. All Sales are Final unless item is misrepresented. Please contact me prior to leaving feedback if we did not provide “5 Star Service”. The part number alone gives you all the information if this part is correct for your bike! If you are not sure please message me. Unless item is misrepresented.