No, in fact the opposite. The 34 typically is only able to be used with a "mountain" rear derailleur.

The good news is that those derailleurs are available at pretty good prices (like a Deore LX) and Shimano rear derailleurs work the same as road derailleurs.

But, as I typed this I remember the disclaimer I almost always add... except for early Dura-Ace... Which applies to you. I think that you would need to change shifters and RD to go to a megarange cluster. But 7 speed downtube shifters are pretty cheap too. Or you can use the shifters you have in friction mode (if available)