is there a reason you didn't build a full chassis for it from the start? if you're plannin on going to custom suspension all round, you're going to end up doing more fabrication than what would be needed to build a simple ladderframe chassis. heres an example of one in a mini (although rwd only, but would look pretty much the same): http://www.rodsnsods...read.php?t=8290
is a professional engineer doing the fabrication for you or is this a 'homebuilt' car?
for the bonnet-motor clearance, can't you just measure the overall height of the motor and then measure the space under the bonnet of your mini? if there are height issues with the motor, have you considered modifying the sump to be shallower, rather than adding a bonnet bulge? another option is dry sump, but a bit more expensive of course!
feel free to completely ignore this, but i strongly urge you (before anything else) to take to your sierra with an angle grinder and cut out the whole front structure infront of the motor, then remove the guards, and then cut the sheetmetal where the guards are attached at the top. keep grinding till you can fit your fibreglass front over the motor and suspension (you'll need to remove the wheels too). sit the car at a height which gives the sump or crossmember enough ground clearance and then see what it looks like. it has to be done eventually anyway, so i dont see why you havent done it already? if you do this, you'll also be able to sit your radiator and intercooler in there and see how much room you have (or dont have... lol) for those.
by the way, how big is your intercooler? usually 350hp cars ive seen will run 600x300x76 intercoolers, which will be a nightmare to fit infront of a radiator and fan and the motor. an air/water unit would be smaller and could be mounted behind the motor where you have lots of space, but it adds a bit of complexity to it all.
look forward to updates
