Well, when I cleaned up the old 20 ga, I have to admit that it looked better than I thought it would. A little gun oil really helps the old parkerized finish of the gun. So, no PCing needed.
Next, I read all the fine print, of the aftermarket stocks, talked to others and decided on a AR-15 style stock to replace the wood-like one. I bought an Advanced Technology Unit that fits several different guns. Using the instructions, I had to "refine" the 12 ga 870 adapter to fit the 20 ga. The instructions were close, but not exact. I actually had to remove a factory "adapter nut" (it goes into the factory gun body) and "machined" the included plastic 870 stock adapter per the instructions. I used a dremel with a cutting wheel and a air grinder with a sanding roll on it. Taking my time, it came out good and the instructions are very clear and fairly close. Next, I re-installed the "adapter nut" and then had to elongate the bolt hole through the plastic adapter using a scroll bit. To leave the "adapter nut" in, during the instruction "machining", would have been very difficult! This hole is where the stock attaching bolt goes through and attaches the stock to the gun. The included allen bolt was the correct thread and length. Note: Because the plastic stock adapter is for a 12 gauge, there is a "nice" ridge where the adapter meets the narrower 20 gauge gun body. I used a piece of sandpaper to remove this slightly sharp edge. No biggie, but it is needed to help the gun slide through and over your hands and clothing.
Well, you can't have a block stock and a woodlike forend can you? So, I read the customer reviews and decided to purchase the Choate 20 gauge only forend. Most others seem to have to be made to fit, the Choate fit perfectly, however, the tool, which comes with the forend was for a larger 12 ga nut and magazine. No biggie, it worked, but it was not correct. I could have easily made a tool with some metal and a grinder, but as I said, it worked and did not damage the original or new forend.
So, for $85 (I caught the stock on sale at Midway) I turned my new HD friend from mild.... to wild. The next thing needed is a sling and an extended magazine.