Dan, putting a Fox .74 muffler on them is much easier than the SuperTigre, you have to cut the bevel down around the ST stack at the phlange and drill new hole in the phlange inboard of the existing ones. If using the Fox .74 muffler you can simply use the Fox as a pattern and drill and tap the engine for 6-32x5/8ths socket head screws, there is plenty of meat there to do it. If you wanted more squeezing power you could use M4 bolts which have finer threads. I don't fool with tuned pipes anymore, if one of yours is an ABN engine it would respond to a pipe from what I understand. Any of them will turn a 14x6 APC about 10,000 to 10,500 rpm on 5% nitro. They hammer pretty good if you try to go over 5% nitro.