Rebuilding T500 engine

[MontaraMarc]

Last weekend (on Easter) my1971 T500 that I am restoring ate the left piston and wrecked the crank and cylinder. I'm going to re-build it and I've obtained a used top end with crankshaft. The new cylinders have a curious vertical port on the intake side. I think this is a later model designed for more bottom end torque. Can anyone verify this?
I would also appreciate any tips on crankshaft seals and other nuance that I should know about before starting this project

Marc

[Vintageman]

Is the vertical port like some called a "finger port" that is a groove cut into the cylinder wall piston surface side like late 60s Yam YR2 and YR3 for examples? If so, I am not aware of any year T500 that had finger port(s) stock, but can be added after the fact. The largest difference between the early and late T500 cylinder, having looked at few is the intake port timing, Some claim exhaust port timing as well but I have only seen a 1mm difference which I attributed to production tolerance but not sure as I am the intake which is a few mm or more if I recall. Suz really reduced the performance of later T500 after the GT550 came out. I did not notice any difference in torque switching from later to earlier on my 75 but expect the later has more at 3500 RPM and less. However, the torque at mid and upper RPMs is much less and there isn't much of a top end or redline reach on later for it runs out of breadth due to small degree intake timing vs early cylinder. If I were you, I would use an early model cylinder even on a later model T500. You don't have to change anything over stock if you don't want to and still works well. Then no one can tell by looking at your bike it is not stock once installed accept you for the engine has significantly more power and still has a strong low end due to longer intake path on later model vs early.