Going through this drama at the moment. I'm sure it all depends on where you plan on mounting your gearbox.
I may be in a bit different situation than you as I am using the floor plan of the commodore in my FC Sedan, so this dictates where the Gearbox sits, hence where the engine is mounted. My plan is to use the v6 engine, v6 gearbox, and all brake components also. I have a thread on here - FC Sedan 2008 Barn Find FNQ http://fefcholden.org.au/forum/index.php/topic,15305.0.html Which may be of some assistance.
I have been trying to come up with an engine mount design which allows me access to the two nuts on the lower side which secure the rubber v6 mounts to the brackets on the cross member. Last week I was informed what usually happens is straight six mounts are utilised and adaptor plates are fitted to the v6 block to accomodate these. I need to order straight 6 engine mounts next before i can ensure where i want to weld my mounting brackets, but at this stage looks like the Pass mount is right at the rear of the HR cross member, and the drivers side the going to be about 5 back from centre. I have bookmarked this thread as I will be keen to keep an eye on your progress and any problems and or solutions you may come across.
Good luck with your project and If I have any success I will also let you know
Regards
Jason
kerrmit@bigpond.com 
