What are you looking to improve? You mentioned "lighter gear set" and "smoother ride", which you may be able to address on your Peugeot.

If you want to lower your gearing for easier climbing, there are two routes you can take: You can replace the freewheel on the rear wheel with one that has a larger low gear, or you can use a smaller chainring on your crankset up front (which may mean replacing the crankset). Both options have potential consequences with other parts, so it's important to know more about the particular components on your bike. If we're lucky, we could simply change the freewheel to one that has a larger big cog (about $10-20). If we're unlucky, you'd need a new derailleur to accommodate that bigger gear (another $20). Count the teeth on your current biggest gear and let us know what model rear derailleur you have, and we can go from there.

As for smoother ride, the easiest way to accomplish that on just about any road bike is to use bigger tires at lower pressure. What size are your tires? Stock on an '87 Tourmalet would be 700c x 23, which are nominally 23 mm wide. You may be able to trade up to 700c x 25, or better yet 700c x 28 if your frame and fork have enough clearance for bigger tires. Panaracer Pasela tires are inexpensive (less than $20 each), ride well, and are readily available.