If your old gasket look like 12391-MG2-790 you need to order this gasket from XL600R page here
Replica with the same specifications as genuine Honda
Before reassembling with this new gasket, you must check that the fixing threads on the cylinder head are not damaged. To do this, check that the entry of the thread makes a 45° angle.
If in doubt, do not hesitate to install a helicoil-type thread insert
The XL600R 1983 year is PD03-50XXXXX
If your old gasket look like 12391-MG2-790 you need to order this gasket from XL600R page here
Replica with the same specifications as genuine Honda
Before reassembling with this new gasket, you must check that the fixing threads on the cylinder head are not damaged. To do this, check that the entry of the thread makes a 45° angle.
If in doubt, do not hesitate to install a helicoil-type thread insert