I have adjustable end links for a 90-97 Miata. You can find more information about them here: http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1,1&item=8075333060&sspagename=STRK%3AMESE%3AIT
These are specifically made for the 90-97 model, but will work on 99-05 Miatas also. Although you will need to buy 4 10mm bolts and 4 10mm nuts. If interested, contact me through a PM and I will be glad to give you the exact specs.
The rod ends have a static radial load capacity of 6200 lbs (using a 20% safety factor).
I have been using them on my CSP Miata for about 6 months now without any problems.