Thanks for all the replies guys, sorry I have been a bit slow to respond. I never seem to do anything other than work lately! But on the plus side it is helping to pay the bills.
I like the idea of plating the rear arms, I will investigate what I can do later this week. Dave - do you have any pics of what you did to reinforce yours? I couldn't see any in the thread on your car.
Is it worth doing anything other than sump guard for the front end? Ie I assume the front arms it isn't worthwhile reinforcing them? Is there any areas other than the engine mounting points that require reinforcing on the body?
Plan currently is to fit rubber sheeting under the body to protect it from gravel, particular focus being on protecting the silly fuel setup (who puts a fuel pump outside the car?), and also the inside of the rear guards, along with some sort of diff shielding. Anything else I need to consider underneath?
As for the suspension modifications, in NZ rally cars have to be road legal, which requires a 6 monthly examination of the car. Things like fitting height adjustable suspension or cutting up structural parts of the body (such as adding in turrets), requires an engineering report and xraying of welds... So I will have to weigh this option up over time, as I don't really want to spend most of my modification budget on certifying the car is safe! From a technical perspective, I have no issue with cutting the car up or having a friend who has the technical abilities to do so, although I am thinking it would make more sense to do this once I had a strut to work with, to work out packaging and positioning of the turrets.
Perhaps in the interim, when the cage goes in I make sure there is room to expand it to support turrets later on, rather than using it to brace the existing ones? Mind you, I can always cut and redo bars in the rear of the cage to suit, as long as the legs going back from the main hoop aren't impacted.
I was thinking maybe do something like this in the interim:
As for the cage, does anyone have any pics of the sorts of cages people have used in an E30 for rallying? In NZ we don't use the bent out NASCAR style bars (they can't be homologated as far as I am aware), so I am looking at going to a fairly traditional cage design, similar to what is in my GTR:
But with the addition of a sill bar and some triangulation between the struts and also a wheel collection bar in the front guards to stop a wheel entering the cockpit during a sudden stop.
Only problem is there isn't an awful lot of room in an E30 interior for fitting two seats and a cage!!!
Z3M parts might be a hard task to find in NZ, we have a tiny car market (only 4 million people in a country the size of the UK), mostly centred around japanese cars. So finding less common beemer bits is nigh on impossible! So I think initially I will keep with the E30 suspenders right now, however the E36 bits seem really like a logical upgrade, so thanks for the suggestion!
Only downside is the change in stud pattern to another really uncommon design!
Thanks for all the advice so far, it has been quite helpful and I have spent quite a few hours now reading through threads on here to find ideas!
Now, back to finishing tidying up the drivetrain. As it is quite stock, the 4.45 locked diff has certainly helped, but I am discovering it and the solid engine mounts is making the car vibrate itself to pieces! So going through replacing anything that could end up coming off the car at a bad time.