when taking a 1272cc to a 1341 you are oversizing the bore from 75 to 77mm.
A few argue that the accralites (£600-650) are the best make of pistons for the money but not the most suitable for the g40 application as they raise the compression ratio from 8.0:1 to 9.0:1. this is not ideal if you intend to run high boost etc but not so bad if you can keep the burn temp down cos it will help with driveability and lower range response.
The better option it seems, cheaper, easier and safer (engine wise) are the wossner pistons. They keep the Comp ratio the same as standard (8.0:1) and around a year ago was quoted £440 for a set...
...This is just what seems to have been the general concensus when i posted up a topic on the matter over on CP... hope it helps!