Rocky, if you are worried about selling it, with those things missing or broken, no real big deal. Midway has a reproduction butt plate. Product #: 653576 Manufacturer #: S14 Our Price: $14.29
Grip gap. Right now out of stock Product #: 512797 Manufacturer #: S77 Our Price: $9.49
One thing to remember is to measure the spacing on the butt. I belive for a 20 ga. it is very close to 2 3/4" center/center. The only way to do it right is to mount the new buttplate on the stock and start filing, naturally being careful of the wood. When you get close to the size, tape the stock and continue until you hit the tape and then be very careful. Even then the buttplate will be a little proud. I've found the best way is to don't use any tape and get it flush with the stock and the right angles and then touch up the stock or re-finish it along with the buttplate. Same thing applies to the grip cap. No one sells a buttplate or grip cap that fits perfectly or even close to looking right. Good luck and keep us posted.