I'm guessing you have the engine torn apart enough to see the scratch? If so take the block to a machine shop and they can tell you if it can be bored out enough to remove the scratch, pistons are available in up to .040" over in diameter which is almost a millimeter, if the scratch is deeper than .5mm or .020" you are going to have to replace it most likely, not sure if cylinder sleeves are available for the 1.3.
BUT, for the most bank for you money, find a 1.6 8 valve or 16 valve motor. Both can be swapped into your Sammi with some modifications. go here to check out the basics of the swap. I'm in the middle of this right now. I'm a newbie too so it would be best to search for more info on the swap so I don't mistakenly give you any bad information...
Check here:
http://www.zukioffroad.com/Tech_Library/engine_swaps.htm
