First, the older models will not fit.
Second, do the 90 and 93 both have the same headlight now? Or does one/the 93, have the headlight/foglight style?

There is an ecode for the one piece plastic headlight that you probably have on the 90. It's only available in Europe however, so you have to find someone who has them for sale. There are two guys on TB who sometimes sell them, MrBorrie and Ben...something, I can find them if you can't. Here's pics
http://forums.turbobricks.com/showpost.php?p=3436766&postcount=17
http://forums.turbobricks.com/showpost.php?p=3442700&postcount=21

You can also convert to, see below.

The fog style has its own ecode design. Those are available as an aftermarket item from FCPGroton,(but apparently they come without bulbs, and you have to get turns separately, which do not match US turns) or you can get factory originals also from Europe. These can be adapted to the non-fog front end, by getting some JY sheet metal and doing some wiring.
RepairmanJack just did this exact swap/install which he wrote up on here most excellently, last month or the one before. There are some minor cosmetic-y details but to most they aren't noticeable.
http://www.brickboard.com/RWD/volvo/1502276/940/960/980/V90/S90/convert_usspec_wo_fogs_ecode.html