Is there a difference between 夂 and 夊, radicals 34 and 35 and 攵, Kangxi 66?
Yes. There is a difference.

There is a fine discussion elsewhere of Kangxi radicals 34 and 35, 夂 zhi3, "walk slowly" and 夊, sui1, "go."

It is incorrect to say that they are variants. They are modern descendants of different characters and their appearances today are far easier to confuse than they have ever been in the past. Whether "walk slowly" and "go" are similar or different in meaning is a matter only of opinion, and the plausibility of any arguments made would depend upon the contexts summoned.

The most common radical resembling these is Kangxi #66,攵 or 攴, both   pu1, "tap." Hanzi which need walking or going in their make-up are much more likely to use 彳, chi4, or 廴, yin3, I would have thought, but this is my uninformed opinion and I would love to see some of the good statistical work going around.

The "tap" radical, Kangxi 66, is different in both meaning and history from the two above, much as it resembles them in handwriting. It descends from 攴, pu1, and even in handwriting it should but doesn't differ from 34 and 35 in that its modern form is four brushstrokes, not their three. (Dian-heng-pie-na vs. Dian-wan-na, is it? The 永-based theory of the brush strokes would have it that they're all four strokes, but they obviously aren't.)

The differing ancestries of all three become clear in two different ways. Wikipedia and Wiktionary conveniently offer the Japanese, Korean and Vietnamese uses of all three and they are clearly distinct. Within the various Chinese orthographies and authorities, the similarities of handwriting are demolished by the utterly different Cangjie inputs.

Wikispaces, sadly, is gone now. It was closed down to a mere marker toward the end of 2018 after a brief but very fine run. 

"Canjie" deserves a capital C in all these sources since it is an adjectival form that stems from a personal name. The eponymous 倉頡,    Cāngjié, was nominally the inventor of the Chinese characters. He is said to have done this in 2650 BCE but this date is clearly approximate, among other things because the date of Jesus of Nazareth's birth is not known exactly.