Idler pulley/tensioner question 1990 5.7 with AC

[RShrimp]

1990 C1500 with 5.7 v8 and AC. I need to replace the idler pulley on the tensioner which should be a no brainer but having a part ID issue.
Parts lookup calls for a GM 10129560 which crosses to Dorman 419-610. OK but those are smooth pulleys with no flange. The one on the truck has side guides or flanges???? Question is: Is the one currently on the truck the wrong one or did I but the wrong one?
Pic 1 of truck and pic 2 of new pulley

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[Nad_Yvalhosert]

Possible that the OE pulley is superceded by a common idler pulley?
The truck is ~35 years old...