More E/655 grips on eBay...with ink marks BUT also with 2-digit SN stamping as well...
I was really excited to see "58" but then forgot your gun has "98"...
http://cgi.ebay.com/ORIGINAL-WW2-GER...QQcmdZViewItem
This other grip of the pair seems to have a much longer number inked in...maybe a SSN ???