JHT: Though I have handled the newer versions, I only own the older, steel receivers models. But there is one difference between the two that I can point out to you.
The aluminum alloy models, produced from 1995 on under either the lightning or lightweight name, also have a folding hammer, which supposedly acts an additional safety. This hammer design precludes the use of a hammer extension, which I have on all of mine and find quite useful.
I find my BLRs to be well-made, quite accurate and sweet-handling firearms. The triggers are heavy and have a lot of creep, but this goes unnoticed in the field.
1977 .358 BLR
1980 .358 BLR - original owner
1987 .243 '81 BLR
1991 7mm-08 '81 BLR