RE: Mini Pipe Section Drawing?
Terry the trick is to come up with a mouse can with threads. Using a Macs header pipe for particular engine, you just slide silicone coupler over header, then screw on can over the silicone, this is all thats needed to hold can securely, Then some 1/4" or 5/16" aluminum tubing makes for an exhaust by gluing it into can with JB weld in center or side as needed . I flare the tube end and put JB weld on flare and insert via inside of can center then add fillet external.
You can actually start with the header at its longest length and it generally is within 3/8" - 5/8" from rear of can, then run and tune, then cut an additional 1/2" off header, run retune to this range from rear of can. The can is no science its just tuning it to what you have to work with.
On Webra .32 the cans can add minimum 1500rpm with poor tuning and 2000+rpms with optimal tuning if you keep at it.
Generally speaking a .25 motor worked on a shorte pipe than did a .32. .40's were longer yet.
Don Miller of AL, is the inventor from competition fun fly days and gets the cans, The article you may refferance is a differant home brew in which cans without threads are used. The MAc header is the costly part of Dons setup which is all I used.
Don hangs out at RCG under the nickname Miderror