Yup I too ran aground when ordering a piston from fleabay.  It was a later Asia model piston that arrived just as has been said.  big difference.  Like a fool I spent some time smoothing out the transfer ports BEFORE I compared them side by side.


 

You can still make a 78-81 monoshock DT125 into a 175 by swapping top ends from a 78-81 monoshock 175. 

Wow thank you for the info! I think the ports did line up on the newer 125 cylinder and it sealed up perfectly with the cases. I will pull it back apart and get some pics up for future users. I would imagine the newer cylinder with the blaster reed valve would be a performance upgrade over the original 125 cylinder too. Had i known what i know now before starting i probably would have gone the older 175 cylinder route, but if this works and is a little performance boost, good enough for me.
Massive help, thank you guys so much!