On my last roll of Rollie IR 400, I tried the D76 1:1 dilution for 8 1/2 min (add 40% time to standard 6 min for stock solution), and I this time does NOT work well. There were tiny white spots all over each scanned image from the entire roll. Maybe there is good reason you don't see any Rollei recommended times for for D76 1:1 dilution. I have a blown-up section of a 35mm frame, and if I figure out how to upload the image I wil do so.
I think I'll stay with 6min D76 stock for now, or go with Rodinal as an alternative.