Porsche was involved through their consulting arm, they also assisted with the 850 5 cyl and its descendants- the s40 4cyl and the 960 6cyl.

I don't believe Cosworth was- they did the Mercedes 2.3. Volvo did not see fit to use a trick intake manifold that allowed the engine to run on only two valves to a certain rpm like most all other 16v designs- this hurt the bottom end power. Also they specifically needed the design to meet the toughest pollution limits out there- this ended up hurting the high rpm power. Also, in view of the need for a quiet low maintenance design they put in hydraulic lifters, which didn't allow them to use an aggressive cam, and also required unsuccessful oiling system mods. Sooo, it wasn't much better than a 8 valve with stock ports, and not as good as a ported 8 valve. But if ported and fit with replacement buckets it can be a good rally head. There also exist two other castings for race use. One is still available from S.A.M in sweden, and the other is an austrian designed (& made??) head used in early eithies rallying.

Thanks to mike aaro of uniteck (and the turbobricks board) for teaching me most of what I know about this issue.