Why is it that when someone asks a simple question somebody always has to make a snide and uncalled for reply??
+1, btdtst. But, then again, some of the folks here get snide, just because.
To the main question: IIRC the Merkel model 8 was the low end of their line during DDR times. Please check the proof date on your gun - it'll be 3 or 4 numbers on the barrel flats, the month and year. Also, look on the hooks for a Q1 mark, often stylized with a triangle. The Q1 stands for first (export) quality, another sign of their best (Combloc) workmanship.
If the last two numbers of the proof date are less than 90, it's a DDR gun and no great harm to value will come from the kind of redo you're talking about. Do not expect a DDR gun to handle steel shot, though. They were not made for it.
There's a good bit of meat in the barrels of the average Merkel/Simson/Thalmann boxlock from that time period so, without looking at the gun, I'll speculate you can open the chambers safely. The final determination on that will have to be done by a good smith.
If you're going to shoot anything bigger than birdshot, though, you're going to have to open the chokes. As I understand your intent, i.e., that this be a hog gun exclusively, you may want to go to a straight cylinder and lengthen the forcing cones, too. Even so, as noted upthread, this kind of use is going to be very hard on the gun. If you have any kind of choke in a double and put tight-fitting, high velocity slugs through it, you're very likely to put bulges in the barrels and may even separate the ribs from the barrels in that area. This does not apply to Brenneke slugs - they were designed and made for German guns with their tight chokes, to be used on wild boar and other large game. If you get some Brenneke slugs and use them, you probably won't have to get any gunsmithing work done at all. Also be aware that you are going to have to check the regulation of your gun - the relative points of impact - to make sure the loads you're using will shoot where you want. You may find out that loads other than the ones you currently intend to use will be more accurate. I'd make a point of checking that it hits both barrels where you aim before going looking for trouble with hogs.
All that said, if I were going to do something like you're proposing, I'd get in touch with Mike Orlen of Amherst, Mass. and kick it around with him. He's got a very good reputation for both the quality, price and speed of his barrel work (but not bluing). I've dealt with him on one gun and was quite satisfied in all aspects. You can google up his name and it will bring up his price list and contact info. Be sure to join the Shotgunworld site and let him know you post there, too - you can get the dealer prices if you do.
