Bouncing of the ceiling even if white won't give you much. I would cross light with a couple WL 1600's at 30' from the head you will likely only have a meter reading on 5.6 with 400 speed film. Inverse square law! 1/1000 shutter??!?!? Leaf shutter in Hasselblad only goes to 1/500 and with a radio slave works only at 1/250.... 35mm top sync is 1/250 at best... and 1/160 with radio trigger.