Chambered mufflers are usually a big jump from the stock muffler as far as loudness. Ever considered a perforated style? The Magnaflow 12589 is pretty much the standard for "a little more than stock with no "in-cabin" noise. The next step in aggressiveness from that is the Magnaflow 12259. AP Exhaust makes copies of these mufflers for half the price. Their XS2589 (Magnaflow 12589 copy) is $64 and their XS1259 (Magnaflow 12259 copy) is $50 on Amazon. The "stock-like-but-a-little-more" is 22" long and the other is 18".
The Stock muffler is right about 28" with a center in/offset out configuration. If not welding it, I'd slip the stock exhaust inside the bigger aftermarket muffler's pipe and clamp it down. Cutting some slots in the 3" pipes (the ones coming out of the ends of the muffler) will let it clamp down more easily. You'll need pieces of pipe to make up the difference in muffler body length, so getting some 2.75"-3" adapters (reducers) will help with fitting the size and taking up some of the extra space.