On the knife you have pictured the handle is attached by having a nut silver braxed on the inside of the buttcap,then either a bent tang with a threaded end onit--or a bolt solver braved to the tang and then bent enough to match the buttcap--or one other way is to thin the end of the tang and then put a cut in the end of a threaded bolt that fits over the thinner tang then drill a hole through both and insert a pin and slightly peen it making a movable joint that will allow for the buttcap to be at a angle and still thread onto the tang.Then when ready to fit up the handle for the last time,just fill the handle with epoxy then screw on the buttcap and that sucker isn't coming off ,no way,no how..
What you are describing with the two halves is a mortise tang construction,Yes you will see a definate grain difference unless you allow enough material and the grain is such that you can match it back up (at least close) but this is not looked down on as long as the seam is straight and inline with the blade.
If you don't want a pin in the handle and are using a material such as stag,do as Rlinger has suggested,and if you want a buttcap just siver braze a screw on the buttcap and then drill a hole for it to fit into and epoxy it in also,this will last a lifetime also.
Just my learnings and not the only way to do things..
Bruce