For a 3/8" stem valve?

Thing is these are the retainers I need to use with the cam I want:

http://www.summitracing.com/parts/cca-747-16

And my heads already have new std size 3/8 stem valves but they are 3ple groove.

Other option would be to find a similar retainer that accepts a 7° lock and use my stock valve locks????

However I dont know if it would be adviseable to use stock 7° valve locks with a MP 284° ,528" flat tappet solid small block cam.....