I'm having a hard time believing Walker ran a 22 mid 200mat anytime in his career, unless it was hand times with a rolling start, especially considering his fastest listed 400m was 48.9?
Snell's fastest 440 hand time was 47.9 for a relay leg, which is what 47.6 for 400m? For an open 400m it would be slower, around 48 flat. He was clearly faster than Walker, but I doubt he goes faster than 22.7/ high from blocks, and possibly 22.5 on synthetic.
Ryun never ran a 46 flat on any sort of track. He ran many 440 yd relays in his best years of 66 and 67, and the fastest he managed was 46.9 hand timed, which equates to 46.6 for 400m. That's worth about 47.3 for an open 400m on a cinder track, so maybe 46.6/46.7 on a synthetic one. Interestingly, in Mel Watman's 'Encyclopedia of Track and Field Athletics', Ryun has a listed pb of 21.6 for a 220yd relay leg! That's about 21.4/ 21.5 for a 200m relay leg, which is surely outside 22 for an open 200m from blocks.
Ovett never had concurrent 21.7 and 3:30 ability. He was a teen of 18 when he ran 21.7 ht for 200m, and at the time was capable of 47.5 for 400m. By the time he was capable of 3:30, which I'd say he was from 78 to 83, his 200m speed was no longer as good as 21.7. During that time the fastest 400m ability he showed was 46.8 in a relay from 1979, which equates to around 47.5 open. He actually ran a 22.9 for his Brighton club in the August of 78 (just before winning silver and gold in the European Champs). By the time he was running around 3:30 I'd doubt he could still break 22 flat for 200m, maybe 22.3.
Cram stated in an AW interview at the end of 85 that his fastest 400m time trial was 48.1, and that he'd improved his speed down to be able to run 23 low for 200m with a rolling start. That would suggest no faster than 23.0 from blocks in a race when fresh. That's why I think a peak Walker may have been able to match that over 200m, but be slightly slower than Cram over 400m