I have a 68.50 t Rex I just did got it cheap and ported by k n t , my engine builder has a 72 bored to 74 right now , u need to trench the cases for the crank and open the top cases for the sleeves , a lot of people don't like em cuz they'r old outdated and some people I don't know why could never get them to run right , but let me tell u these in the right hands fucking scream , my bike won't take shit from cubs or cheetahs , and my builders is racing DM bikes w bigger strokes and teArs shit up , only suggestion I would make is yes since they'r old and out dated try to look for the best deal meaning cheaper than cheetas cubs dm or whatever other competitor Cilinder , also cuz part are getting a little bit harder to find