Hi Andrew , the biggest size piston to safely go into a pinto is 93mm , maybe 93.5mm if the block is in really good shape. There is pistons to suit for sale in USA cheaper than UK , being for the cologne v6 2.8. You might need to buy all 6 in the set but it's still cheaper .
Once you've got the 93mm pistons the block will need decking about 0.040th to bring the pistons to the top. ..or do what i done and get the crank offset as much as possible and then get the block decked. Mine became a 2176cc with the above done and with some decent head work it had 116kw at wheels on twin 40 webers..