Hi Nitrous SSC:
There are numerous posts on this, but I'll give you a summary. Spacers can be broken into two categories.
There are spacers that are designed to fit over the wheel studs and simply sandwich between the hub and mounting surface of the wheel. I call them through-bolted type. Typically, these are about 1/4 - 3/8" thick or so. Any thicker, and the wheel nuts won't have sufficient thread engagement on the studs. Regardless, these depend upon the studs to accurately center the wheel, which is not the most accurate method. This can result in excessive vibration. Also, they put more bending load on the outermost end of the studs, which might lead to failure.
The other category of spacers are generally 1" thick or more. I call them bolt-on type. They have holes machined in them and come with a set of nuts so that they can be bolted up to the hubs. They also have a set of studs pressed in so that the wheels can be attached directly to the spacers. Better quality ones are machined to accurately center on the hub flange and have a machined lip to accurately center the wheel. These are called hubcentric. Generally, hubcentric spacers like these are considered far stronger and safer than through-bolted spacers. In my opinion, you should only consider this type.
More to your question, 1/2" spacers will be difficult to pull off, because that is too thick for the through-bolted type, and too thin for the bolt-on type. You could have something custom made, and install longer studs, but I wouldn't recommend it.
Some will say all spacers are bad, but I have experience with hubcentric spacers (on my Mustang), and they work well if they are made correctly. I recommend H&R spacers. Perhaps you could live with using 1" thick hubcentric bolt-on spacers.
Other than the failure and vibration risk with using cheap spacers, the only other real issue that comes into play is if you change the effective wheel offset significantly from stock. If that happens, the wheel bearings will see much higher loads, and probably fail prematurely. However, it sounds like you will be moving your wheel offset closer to stock than they are now, so you should be fine.
Incedentally, some people refer to bolt-on spacers as adapters, just in case you want to expand your search a bit. Technically, though, adapters are spacers that are used to change the bolt pattern so other types of wheels can be used.
I hope this helps.
Regards,
John.
