Can someone confirm that the MK Indy R chassis is made for the 7" Sierra differential and not the 7.5".... Or are they basically the same mounting points?

yes 7 inch fits MK Indy. If it a cosworth get viscous unit pumped up ( try Phil Jones Engines). If you need to change the diff ratio contact Kamdiffs, i just took delivery of a 4.4 from them. I am fitting a 6 speed quaife g60 gearbox

I thought the indy R's transmission tunnel would be too narrow for the gear box?

[Edited on 8/8/11 by MikeFellows]

When you order a chassis from Mk they ask you to specify if you want the mounts for a 7'' or 7.5'' sierra dif, so it could be either.

Thank you, I confirmed tonight that it is in fact a 7.

Apart from Quaife, who else makes a LSD for the Cosworth, after reading a little I am not very impressed with the factory LSD.

if you want to fit an aftermarket LSD you'd be better looking for a normal sierra open diff to put it in

the ford LSD's have unequal lengths of the stub shaft's - all the aftermarket ones I know of need equal lenght ones from the open centre diff

quaife, tran-x, gripper diffs are all options or you could even get the ford LSD 're-tunned' be filling it with different fluid
(flak monkey fitted a tran-x diff to his, he's got a few threads on why he picked it and how to fit one)

there are quite a few old threads discussing the pro's and con's of each type:
http://www.locostbuilders.co.uk/viewthread.php?tid=147258