Yes go for it.
Swapping the shock will make it ride a lot better as it lowers the bottom bracket and slackens out the head angle, as well as being a better damper.
Oh and the e13 should fit, I had a mrp on mine.
there was a artical in dirt (july/august 06) on what the top pros were running.
Its a bit hard to read but you should be able to get the jist of it.
Rennie and Peat ran push internals in the 06 season and most proberly still do.
I love my cut down 2.5 super tacky wetscreams, There mint in conditions from rutted slop to loose soil and they grip roots and rocks like highrollers.
But when the dirt drys up and starts to get hard they roll super slow and squirm in the corners.
My hayes 9's have worked fine for the past 2 years.
I've bleed the rear once and havent bleed the front at all.
With one finger on the levers i can pull stoppie's at any speed so they have plenty of power for general DH use.
The levers are getting a bit sloppy but they still work fine.