HI Greg,
Built straight and not too heavy, the stock Twister will fly extremely well. You can go ahead and do the "mods" but maybe a straight out of the box build will suffice for now.
For the LA .25 I will suggest swapping out the remote NVA for the OS parts that are for the older FP series, they are a direct swap and available from Tower (the parts numbers have been listed here many times). Venturi and NVA is all that's needed there. I would also recommend swapping the plastic back plate for a metal one. Curtis Shipp, a member here, makes excellent back plates for this. I have seen too many of the plastic back plates leak on the LA series when running them in stunt planes so a bit of aggravation can possibly be missed by the swap.
After a couple tanks of "break in" (they really do not need much break in at all), I would use an APC 10-4 and set the engine just back from peak. Running what's called a "wet 2" cycle. A very consistent run that produces plenty of usable power. Just try not to build the Twister too heavy!
I wouldn't try to get it to 4-2 like a Fox .35, it defeats the purpose and won't be easy to achieve with the LA engine's timing. Any good fuel with about 10% nitro and 20-22% oil, 1/2 and 1/2 castor/synthetic seems to work best, and use a good "hot" plug.
Big Bear