No idea what rear main seal style has to do with pan selection. Unless you think you might have a 273/318/340 block, the rear main cap and corresponding rear pan cut out is the same for 360 and 5.9 and also 5.2. If my memory serves me correctly.

BUT...The one piece magnum style oil pan gaskets are not meant for use on older LA style oil pans. So you have to use a 4 peice kit or modify the pan itself. There are two slight kick outs on the the front of LA pans where it meets the circular part of the timing chain cover. The magnum pans didn't have this and using the one piece magnum gasket will leave those spaces open and you'll slosh oil out the front every time you come to a stop. There was a prior thread on this two that showed the differences in the oil pan edges there.

Probably obvious, but make sure to get a pan with the right sump location.