Hello Gatchaman, and welcome.
I couldn't tell from your post if you have your heart set on the Scan-dyna A30X speakers, or are just considering them. If your ST-35 has he eight and sixteen ohm tapped transformers, and you do get the four ohm speakers, just run them off the eight ohm tap. You won't hurt anything. You could invest in new output transformers, as Captain Coconut suggested. But the differences I've heard between using the eight and sixteen ohm taps with my eight ohm speakers just wouldn't be worth the price and work involved in swapping output transformers.
If you haven't decided on speakers yet, may I suggest you consider The Horn from The Horn Shoppe. It's a single driver (no crossover) speaker, an easy eight ohm load, 94 or 95 dB efficient. If, like I did, you think a 4" driver can't do rock music justice, I understand. That was until I heard them, I mean. They cost $850 per pair, delivered to your door, and you have thirty days to see if you like them.
There's plenty of reviews on them in Stereophile, Six Moons, TNT, Positive Feedback, etc. if that means anything to you.Horn Shoppe reviews
I have no affiliation with the Horn Shoppe other than being a satisfied customer and music lover.
Good luck with your Dynaco equipment and whatever speaker you end up using, please consider the $10 EFB bias mod for your ST-35. It will allow the amp to provide more power for the speakers, it will make your output tubes last longer, and it will sound better!