Alpines in raised bed

KT53

I have a raised bed beside the patio.  It gets sun for a couple of hours in the morning and all afternoon and evening - during the summer months.  In the winter months it is in shade pretty much all the time.

I put a couple of hebes in there while the garden was being stripped out and they have done well, too well, and I will be moving them as they are too big.

I'm wondering if this would work for alpines.  It's very well drained as the bottom 9" or so is filled with rubble.  I will need to top up the bed by about 6" to make up for where the soil settled over the past couple of years.  If the location is suitable for alpines, what sort of soil / compost mix would you advise?