Converting your private key will result in a completely different address. Electrum should be able to import any WIF private key.
Well I have a paper wallet with a private key beginning with a 5 (WIF format) but Electrum 2.6.4 seems only to allow to sweep private key beginning with K or L.
When I try to enter my privkey beginning with a 5, I cannot click on the "Sweep" button whereas I can click on that button when I put a privkey beginning with K or L.
Doesn't 5 at the beginning mean it's encrypted? I guess you've already figured it out, but next time you could always see different values by inputting them on
https://www.bitaddress.org if you have any troubles. I'd suggest downloading the website and doing everything offline for added security.