I put the LS6 heads on my 4.8 but I had them milled 035" netting me around 58cc.
Your 5.3 heads combustion chamber is around 61. something cc and the LS6 are 64cc
Not a huge difference maybe you could go with a thinner head gasket and get it close enough.
I love theses heads, it made a big difference. IMO I think you would be very happy with them.