Gimme a break - I just saw this one! I've been up to my ears in C Programming homework all evening...
I can't swear to the 2.46 (remember, I play with REAL engines - I stick to 4 cylinders for my lawnmower... j/k) but the 4.0 uses 3/8"-16 there and I see no reason for the 2.46 to be different. If you have a well-stocked local or a marine supply store handy, you should have no trouble finding them in brass - which is highly recommended for undercar exhaust... I've been using brass for undercar exhaust joins for just over 20 years now with no ill effects...
If you get a 2.46 apart anytime soon, I'd appreciate input on bolt sizes to both confirm they are/are not the same as on the 4.0 and add them to the worksheet. Thread pitch, overall length underhead, and grip & thread lengths, please.
5-90