I’d either FULLY rebuild the head you have or try to find a late 693 JD with oil bath, hyd deck plates, poly and a full Calmer kit on it.  

Or if you really want to spend some money, go buy a new Drago.  



Your 863 can be rebuilt into a very nice head if you’re willing to put time and money into it.     In addition to all of the normal parts, I’d put the following parts on it.    
New keyed gathering chain drive shafts in the gear boxes.   
9 tooth gathering chain drive sprockets, Calmer used to have these, not sure if he still does.  
900/1000 series gathering chain guides
JD 40/90 series gathering chain tightener apparatuses and idler sprockets 
New poly snouts 
A new 1 piece hex drive shaft through the gear boxes, this requires a new pass through drive hub to be installed in 5 of your slip clutches 
 Build (or buy and make it fit) an oil bath cover for the chain 

Here’s a link to an old thread from when we built a 20” head from 800 IH pieces.

https://talk.newagtalk.com/forums/thread-view.asp?tid=212116&DisplayType=flat&setCookie=1

It was a good head but we moved to a bigger combine and now run a 1290 JD with Calmer parts on it.  The Calmer parts really make the 90 series JD heads work good.   If you could find a good 693 with Calmer parts already on it , I’d lean that way.  Finding a used adapter plate to put it on your combine isn’t too difficult.