I don't think you can lock the trans in LU in 2nd gear, there is a valve in the lowest section of the VB to prevent this, it would need to be blocked in some certain position to prevent it from overiding the fluid being blocked by the solonoid.

As for towing, you could certainly stroke it to a 408 and gain a ton of tq without doing a bunch of other mods, just bumping the compression and getting some quench not to mention the added cubes is going to do wonders for TQ production, I built a 318 into a 392 for a customer with a stock cam and lightly ported heads, not even a CAI or upgraded exhaust and it added a mountain of TQ.