Half way through build and I decide to drop live axle and go IRS!! ... typical, I don't think that there is going to be anything that end up the way it started!

So I need a bit of advice ... It seems that Sierra Cosworth LSD diffs are the things to use but What is the difference between 7" and 7.5" ?? Which is best ? and why does there seem to be such a price difference? What are the factors to look out for?

Also are these uprights on ebay any good?

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=230385538383

They are narrower across the lower wishbone mounts than the McSorley plans show. Is this a problem?

Uprights no good for fitting drums there... 7.5" diff is a lot heavier than the 7"

I was thinking of inboard discs.

but ... I have heard somewhere that the sierra diff has weak bearing housings and they cannot take the loads that an inboard disc set-up will create.

Is that right? ... has anybody done it?