We've changed out a bunch of these for folks and like Brian says it's unlikely you'll find an easy adapter (though there is one for going the other way around...but not many remove an SL and put in an IC). Regarding the radios, feature sets are good in the IC, but long/mid term reliability of them has shown to be lackluster at best when compared to the SL's. The design of it (like the little ribbon cable) lends itself to more trouble than the SL, but if you didn't have to remove the faceplate and the cable to remove the radio (or have to remove the radio ever at all) that wouldn't be an issue.
That being said, the older 200's are still going strong and from a robustness standpoint they seem to be holding up better than the 210's. The 210 can also have an issue where it moves a little bit off frequency in certain ranges sometimes. True that both can and will have a small percentage of lemons out of the box....but overall the SL's just surpass the IC's in that regard.
Anyway, not arguing either way just pointing out what my take on it has been (and we'll gladly sell you either).
Just my 2 cents as usual!
Cheers,
Stein