I think your main problem with ladder beams (and most kit to be honest) will be trace-ability
There are so many types, 305 c/c 305 O/A Depth, full saddle welds, spade ends not to mention various crs for the rungs.
When you talk about manufacturers recommendations you may still have issues, not so long back I bought alloy beams from a reputable manufacturer only to find they had subbed out the manufacture of their beams to outside contractors one in the UK, a very reputable supplier and the other in Eastern Block Europe.
Weld tests failed 20% of the UK and 100% of the Eastern Block Beams.
The point being you know not from whence you beams came!!