Hi Hoser, I finally had time to go dig up the FL250 piston interchanges for you. Here's the info:

  The following pistons are a direct interchange with the FL250:

  73-74 250 MT,CR,MR - Does not have reed cutaway

  75-77 250 MT,CR,MR - Does not have reed cutaway

  77-84 FL250 - Does not have reed cutaway

  78-80 CR250 - Has Reed Cutaway (431)

  81-84 ATC 250R - Has Reed Cutaway (431)

  The list above is a guideline for the piston you are looking for (FL250 interchange with reed cutaway). Since 
you have a reed cage, order the 431 style 
  (78-80 CR250 and 81-84 ATC 250R) and you will have a good chance of getting one with the reed cutaway 
already there. 


  The 78-80 CR250 and 81-84 ATC 250R - pistons are supposed to have the reed cutaway out of the box, 
but I am looking at a Weisco 431 I have that came 
  without cutaway. Don't ask me why, I don't know. It just means I have to cut the damn thing (that sucks, huh? 
Go figure?). I have ordered 431's before and  they came out of the box with the cutaways. 


  All these pistons are available through Weisco. I know you hate Weisco's so I tried to reference them 
through ProX. None of these pistons are available through ProX as far as I can tell. There are probably 
factory Honda pistons available through your Honda Dealer if you want a factory Honda piston. I have 
  not researched Sudco, so they may be available through them (if Sudco & ProX aren't the same co., 
ain't sure).




  Hoser: " I get 2.792 using a snap gauge and calipers I get 2.799 using the snap gauge 
  and 2-3" micrometer I can verify 0 on the calipers but can not find my gauge blocks 
  to verify the micrometer. (wonder where the hell they are hehe) ."


  Usually if I can find my t-gauge, I can't find my caliper or my micrmtr, so you are doing better than me :-)
  According to 1" = 25.4mm. Then: 2.799"x25.4 = 71.0946mm bore on that Mossbarger cyl you have. 
Stock FL250 bore is 70mm. If the bore cleaned up at   2.799 you should be able to order a .050 
(71.25 Weisco) piston and then bore your cyl to match. I think Honda only does .020" increments, 
so a Honda   piston would be a .060" not .050". That would be a 71.5mm bore @.060".



  There is also a KTM 300 piston that will work when you reach a past - .080" situation if you are 
willing to do a little machine work & cannot locate another  cylinder. If this happens to you, email 
or call me and I will give you the details. (That KTM thing is between you & me OK. I can't give 
out tricks, especially if   they can screw up real good if they don't know what they are doing).


  You had asked me about a long rod setup for your FL250 crank. The part # for the 10mm longer 
rod is Vesrah K5464, or Niks ProX 04971, or Weisco/Hot 
  Rod CR156. It is from an 87-89 TRX250R. Marv has told me he will build the rod in Titanium if I want one.


  


  
  Bill..