08 Silverado's came factory with 5.3 and 4L65E. Same size as 4L60E, and the 4l60E is just an electric controlled 700R4 so you will have no issues bolting up. Are you currently running a controller on the transmission or sharing the ECM from the L98?
Guess back to your question, Are you running the exhaust from the corvette? What is the location of your cats? I am running dual cats on my 59 V8 swap and I have one that fits between the trans and brake booster and another that fits the passengers side. Flowmaster makes a nice set, 4" around.
Found a few measurements on the internet. And here is my Cat set up. Not sure if anything I just said will help.
