Hey, my first kit-bash! Thought I'd share what I'm doing here to those who might not as yet taken the plunge in combining two different company's kits.
For the main base kit, I'm using Hasegawa's VF-25 Super kit, since that way I don't have to futz around with trying to fit on the leg armor. You will need to separate these parts out, though. The middle portion is not needed.
These are the Tornado parts you'll need from the Bandai kit. I despise the Bandai Frontier line, that's why I'm putting these parts onto a Hasegawa kit.
Wings? You won't need them. You can also skip the part where you put in the wing mounts/swing mechanism, since you're going to keep the wings fully swept anyways.
On the Tornado wings, you'll need to open the opening up a bit more to fit over the Hasegawa kit.
That's where I'm at right now. When I come to more modifications, I'll update.