Dave (SMSP) doesn't work for Carsound...he sells their cats...he's a custom header builder and makes his own line of extra long hybrid 4-2-1 headers with a 2.5 in. collector and 2.5 in. OD adjustable length exhaust kit. The length on the header (secondaries) can be adjustable too! So he needs to sell a proper cat for his systems. He chose Carsound. He welds on the O2 bung and flanges to the Universal Carsound cats (different models available...see my Article in the Performance Forum). The cats are custom sized to fit any length you need...they fit without leaks...good customer service too.that's why I recommended him or Mike at IPS Racing to the T-I.net members looking for a proper aftermarket cat..they have proven track records and many customers who can vouch for the product they received...all happy....
So yes they are custom made to fit IF YOU DO WHAT HE ASKS AND GET UNDER YOUR CAR AND MEASURE IT. He does not work for Carsound...he chose them independently for a reason instead of Random Tech (see my article on the flow rate of a Carsound vs a Random Tech)...
I hope you take the time to read the cat article in the performance forum...cheers