My thoughts were similar.
So long as the gearbox goes in then the rest can be sorted fairly easily.
There's at least one builder with an XE, may be worth tryign to contact them.
It's a Getrag 240 box
http://cgi.ebay.co.uk/VAUXHALL-OMEGA...item23080f0158
looks quite compact if a little wide at the bellhousing.
TT