If properly restored, they would do not bad at all.
If I compare my E-303x (restored), C-280V (restored by Accuphase) and C-2420, I notice more and more precision and focus in the scene (with the E-303x also a bit noisier, the others essentially silent). But in my opinion the differences in normal listening situations are not, especially the comparison between the last two, "SO unbelievable! Night and day! WOW incredible!!"
In my case, for example, careful room acoustic passive treatment and accurate EQ with DG-58 with a lowly E-303x give better results than the C-2420+A-46 in another non treated room without EQ (I tried many times
).
I stress on the "restored" thing because in quite old units still totally original, the sound probably is not what it was when they were new, so comparison with modern units is not accurate.
My E-303x had a very, very smooth sound, with a graceful slope after just 8Khz.
Yeah, smooth and pleasant, but not what the original project was and too much unwanted and unsettable coloration on the signal.
After a quite extensive work on the unit, now it sounds much more "normal", with a normal frequency response. Maybe less particular, but surely what Accuphase went after when they engineered the unit.