I use the 15W40 Penzoil Longlife in the carb version 99 outback. Unable to find the similar marine version locally. At one point, somebody on the board confirmed with Indmar that this was a reasonable oil to use. 15W40 is noted on the stickers on the motor. ( at low hours, you might have some similar sticker )

The idea of confirming via the manual for your specific engine sounds like good advice. But my 99 Indmar owners manual which only shows injected motors calls for 20W50. So there is a disconnect between the manual and the motor stickers in my case for some unknown reason.

The phone number they say to call in the book is customer service at 901 353 9930 in Memphis ( Millington, TN ). Don't know if it still applies.... I didn't call, just used the 15W40.