NB Bilstein Ride Height issues and questions
 

Alright I have the ebay coil over/bilstein setup. Specifically I have NB Bilstein Sport shocks on a NA miata. I have ebay sleeves and I cut off the tab so they all sit on the lowest circlip. My front springs are 7 inch 400 lbs and my rear springs are 7 inch 300 lbs I have the NB top hat stock assembly with fat cat's bumpstops. Furthermore I don't mind compromising my rough ride because I'm doing HPDE with this car.

My Issue is my ride height is not as low as I would like. Im not trying to get any kind of slammed/CR look. I am trying to get closer to 949's ride height recommendations
(Miata Race alignment).
Ideally I'm trying to 12inch ride height (hub center to middle fender) and 4.5-4.75 inch pinch wield.

I have read a lot on these forums about this setup but still have questions. I am thinking I have three fixes to getting it lower. The first is getting shorter springs. I am thinking I would need to get 5 inch and 5 or 6 inch in the rear.
Here is one site I found to buy them and I know hyper coil springs are good but pricey.
HRPWorld.com - Everything You Need To Build & Maintain Your Race Car.
I found some cheaper 6 inch springs but I would rather be too low and then just use the sleeve to raise it up.
6 inch springs => (6 inches tall - PAC Racing Springs)
If anyone has better ideas about spring lengths please help me out. Im not full set on 400/300 but I do think its a decent setup.

Another option that I have found is the ISC top hats. I know I would have to drill out the top hole to fit the NB bilstein shaft? Also these would give me more rebound with the less shock travel but what custom height would I need these at to get me down to my ride height goals? Would this be a good idea compared to springs or new perch mount? It would need to be close to 2 inches more to give myself extra room I don't want to barely reach the ride height. At a long length of something like 2 inches does that create any structural issues or clearance?
(Miata Suspension)

The last option would be to remove the circlip from the shock body. Then go down the shaft some length and cut a new grove into the shock body. This would be the cheapest to do. I have access to a lathe and multiple mills. I just not sure how far down I would go. If anyone has information on doing this I would appreciate there knowledge.

I have MSM Bilsteins and ISC top hats on a NA miata. I did not have to drill out the top hats for the bilstein shaft. I think ISC's website is talking about drilling out a hole if you have an NB chassis, I don't think there is an issue with the NA chassis.

My problem is I have the stock MSM springs, that coupled with the long dampers = way too high of ride height. In my case ISC tophats won't be enough to make up for it, apparently on an NA miata they equal about 3/4" of a drop compared to the stock NA mounts.

Yeah I seems to be my problem as well. I guess getting the extra travel was not worth if for me because of the ride height and alignment I wanted. Another option I saw was shortening the shock bodies but I would rather save that money for better shocks.