Nizpro mounted both idler and tensioner above the water pump ages ago.
You'll have trouble finding what belt to use though.
And there's no such thing as rb30de block.
Its a shame you didn't check to see if the idler face was there ready to go, all later blocks had it, just early blocks didn't all have it.
Guys have made some adapters and such to get the idler mounted in the typical spot.