420c newbie question again

[ejb17]

Can anyone tell me if I am blind or the couple sets of pictures of some 420c's I have looked at do not seem to have the top idler roller? Also should they be yellow or green and would the serial number help me so I know before buying? Anything else to look for on the 420. Thanks for any info

[Lavoy]

4 roller crawlers never had a support idler, 5 roller always did. Before serial number 100,000, the 420 did not have a yellow stripe, after that, they did. Trackframes, sprockets, and idlers were painted yellow regardless of serial number.
Lavoy