It has been a long time since I owned my D70. ARC amps of that period have a limited range on their bias pots. So the answer is without modification, maybe. Turn the bias pots down and install the KT88s. See if you can turn the trim pots to the proper bias. I never tried KT88s in my D70. I did run them in my Classic 60 and a slight modifications needed to be made so that they could be biased.
The Speaker strips were always a problem. Though I think spades have gotten a little bigger over time. I used Audio Research speaker cables with my D70 so I had no problem. Excellent cables for the money with ARC equipment.
How are the 2 large Capacitors? If they have not been replaced they should be checked. They may need to be replaced soon.