How to choose the light bulbs for a given dynamo
Apparently the 1970s PX-60 (see the OP's comment  had a Soubitez bottle dynamo ("génératrice") on the rear wheel as sold. Similar looking vintage Soubitez dynamos come up on eBay, where sellers and photos both indicate that they're 6V 3W.

However dynamos labelled 16V 8W really did exist: They were made by Sankyo, and again appear on eBay.  They were apparently fitted to Raleighs and Schwinns in the 70s.  If that's really what the OP has, and the output is really that much higher rather than just being an optimistic rating, I could be tempted to try something like a 12V 5-6W incandescent bulb in the front, and 12V 1W at the back, if you can somehow make them fit.  These are cheap as they're used in cars, so getting a couple for testing would be reasonable, as would getting through them quicker than you'd really like.