so im just curious on how much it costs to do this  ( i know it will vary from shop to shop ) im just looking for a rough estimate and where exactly i can get this done at.  im just tryin to learn some stuff.
and can anybody tell me what doing this all entails, upgrades, new parts, modification to what parts? and possible pros and cons

The 79mm pistons are not availible any more.The closes you can get is a 541.Here is the link. http://gstwins.com/gsboard/index.php?topic=14401.0

why?

Not enough demand

the last V&H 555 kit was mfr'd in 93 or 94
there was little demand when the kit came out
also that kit originally came out in the early 80's for GS450 race bikes

if you want more power...go buy a more powerful bike

if you are trying to stay with in the rules of a racing org....you'll figure a way to make it work

I know someone who is using GPZ 85 mm pistons in a GR motor, which he stroked 5 mm by sending the crank to falicon. Flat top pistons with 5mm shorter pin height, then he opned up the valves to fit TL valves, he milled slots for the super high lift cams and the cylider was nikasilled with an aluminum sleeve in it. 851 CC in a GR lower end and into the GS. I suggested the 4 valve FJ head saying I know where he can pick up FJ sprint car scrap. Anyway, MTZ made the pistons for him. JE will make you a piston to your spec, need to just buy 4 for a $650 total.
Cool.
Srinath.

http://www.mtceng.com/index.php?option=com_content&task=view&id=67&Itemid=121

Not MTZ, MTC and that link is to their catalog.
Cool.
Srinath.

The last of the 79's were made in 1992, according to Wiseco when I talked to them several years ago. V&H contracted Wiseco to make them and they hold the rights. I still have 1 of the 79's I happened to come across... still waiting to find another to build another 555. But in the meantime, 80's will do. No idea what bike they are from though.

Yep the best option (without going too stupid) are the 78mm GPZ pistons. 

Now the GPZ's are shorter pin height aren't they, and the ones I saw in the 85mm size were also flat top. The guy had gone to town shaving and lightening the insides of it.
Cool.
Srinath.

They are either the same height or very close. Been awhile since I had the motor apart. These are high compression pistons, not flat top.

Just remember the GS crankshaft is the weakest link.