What was the modification on the old style Enduro frames for the rear shocks? Something about a longer shock increasing the bottom bracket height.

Also something about reversing linkages.

What am I searching for to read more about these modifications?

There was a 'low' shuttle lowering bb height, slackening off the angles and a 'higher' shuttle tightening the angles. I think the higher one was used if you were running a shorter 130mm fork up front and needed to decrease rear shock travel. I've got the Enduro 06 with Fox Talas 36s 150mm up front and the low shuttle giving it a 67 or 68 HA and 160mm travel at the back – not too sure on exact figures. Doesn't seem much point to me running the Enduro as an XC bike though it's not what it's about. Best see Specialized website tech centre.

From memory, I believe some people where running a 8.75 X 2.75 shock instead of the standard 8.75 X 2.5 This upped the travel to 6.something inches and raised the static BB height. The mod only worked with the shuttle in low/slack mode.
Could be wrong, it was a while ago.

read me

and me

How old is "old style"?

For my 2004 Enduro as below, replacing the standard shock with a 200x50mm one (10mm longer than standard but same travel/stroke) and running with the linkage in the slacker position, the BB height was raised just enough to avoid constant crank hits while the head angle stayed spot on too.

FWIW, I also tried it with a 200×57 shock (the DHX air in the pic) which worked fine too and upped the travel to somewhere around 6" but for the riding I do, 200×50 was better.

How old is "old style"?

Oh I don't know. It looks remarkably like your bike there in fact. Very similar indeed.

I know you mentioned that a longer shock was in place, but I couldn't find any info on the benefits of changing the shock and/or the linkage.

I'm a tinkerer/scientist at heart and need to understand why I'm doing something before testing it out.

I've the same bike. Lenghtening the shock is going to make the static head angle steeper but will raise the bottom bracket.

For best results, you could always get the shock tuned. TF Tuned offer a service which replaces the damping piston with good results.

I and many other people found the BB on the standard enduro to be a bit low – meaning that you were constantly catching your cranks/pedals/shoes on things unless you coasted through rocky trails.

fitting a 10mm shock raises the BB a bit but also steepens the head angle. For me, since I was running the linkage in the steeper head angle position originally, changing it to the slacker setting with the longer shock meant keeping essentially the same head angle overall but fixing the BB height.

Fitting an 8.75 x 2.75" shock to an '05/'06 Enduro increases the travel by approx 3/4" & gives you 165mm rear wheel travel, basically you fit an SX trail spec shock.

I have done this to my Enduro & am selling the shock in the classifieds
http://www.singletrackworld.com/forum/topic/fs-hope-90x10x318-stem-fox-dhx30-coil-gives-spesh-enduro-more-travel#post-1644029

I and many other people found the BB on the standard enduro to be a bit low – meaning that you were constantly catching your cranks/pedals/shoes on things unless you coasted through rocky trails.

fitting a 10mm shock raises the BB a bit but also steepens the head angle. For me, since I was running the linkage in the steeper head angle position originally, changing it to the slacker setting with the longer shock meant keeping essentially the same head angle overall but fixing the BB height

I take it that is how it is still with that current shock that you fitted?

clubber, er.. you sure about that?
if you retained the same Head angle, you'll have the same BB height as before.

best thing about the old enduros was the low BB, if you can't get on with it, it's simply not the right bike for you. rather than **** about fitting longer shocks just get something with a higher BB in the first place.

OK, it's not actually quit the same head angle but it's close enough and it raises the BB just enough – it's a tweak rather than a massive change but for me it made the difference between constantly hitting cranks and not.

Disagree about it not being the right bike though. with the longer shock it was spot on and rode brilliantly. Why change the frame when there's nothing that an easy shock swap will fix?