Peugeot 504 timing - 1983 Peugeot 504

The Peugeot 504 XS produced in 1994 came with a range of engine options, including a 2.0-liter inline-four gasoline engine with a maximum power output of 120 horsepower (88 kW) and a 2.3-liter inline-four diesel engine with a maximum power output of 71 horsepower (52 kW). It's important to note that the engine power may vary depending on the specific model and region where the car was sold.

To be honest for the work involved it would be easier to just swap out the 1600cc engine for a complete 1800cc engine. Engine cc can be set by different things. Piston bore, piston stroke, connecting rod length and so on. 1800cc pistons might simply be the wrong size for the cylinder bore.

Peugeot 504 Wikipedia

look at this link might help you out.
Which are the characteristics of the peugeot 504 of the year 1969 Google...

normal for this car ,and most cars in fact

Hi I know this is years later, but removing the thermostat is not advisable. If the car heats up in the summer have your radiator taken apart and the core cleaned by a professional radiator place. The 504's core tend to get blocked over time. it might also be a good idea to try and get a more heavy duty core or make fit a bigger radiator. Always have coolant in your system other wise the water will eat your cylinder head. It also prevents the radiator from getting clogged up.

colud you see the mecanical manual of peugeot 404, in web site of club peugeot 404, version in french

The computers software got bad.