Do you have the heads already? Asking since the good ones have been out of production for a couple years now. Is your LA engine originally flat tappet lifters or hydraulic roller lifters?
The heads will bolt onto an LA engine. I forget if Magnum head bolts need to be used, but I think one or more are longer on a Magnum so probably yes. They do require Magnum style rocker arms. The lifters need to be capable of oiling through the pushrods and the pushrods need to be hollow. The length of the pushrods will need to be measured to determine the length. The LA block deck height is slightly higher than a Magnum, so even if you had an LA block with factory hydraulic roller lifter, Magnum pushrods may or may not be the correct length.