L-1011 Engine Modification? Options

[TWA727]

Hello everyone,

I am here to annoy you once again! Muwahahaha!

While surfing airliners.net for pictures of the L-1011, I noticed a small difference in some Delta Air Lines L-1011's. There appears to be an "extension" of sorts of the cone of the engine. Here's an example:

Delta L-1011 modified

and in this picture, taken earlier this year, there is no modification:

Unmodified L-1011 engine

I do know that Delta had some range-enhancements done on the L-1011 which entailed fitting the -500 series' engines, but still, the -500 does not have this "extended tailcone."

L1011-500

Any insight would be greatly appreciated! Thanks.