Corran should be worse in an X-wing then he was in an E-wing. He wasn't as in tune to the force while he was in CorSec because he didn't know he was a jedi.
He should be - given the precedents so far - the same pilot ability, and since his pilot ability is tied to attacks, and the X-wing has the same firepower, he's broadly equivalent. However, he loses the sensor slot, barrel roll, and one green dice.
The Green dice can be more or less 'written off' because access to the Integrated Astromech free modification pretty much balances it out, but he's demonstrably worse with the same abilty. Therefore He's going to be quite a bit cheaper.
This does not give the shield regen ability that Corran in the e-wing wants but it does make him as close to the e-wing as he can get.
In terms of a game piece, we don't want Corran in an E-wing in an X-wing, though - we want Corran in an X-wing, and for it to feel fundamentally different. Costing substantially less, and essentially being a multishot primary weapon as an alpha strike (on the assumption that he's not going to be able to get away and come back again) makes for a significantly different 'feel' to the E-wing version.
Whistler being an 8 point plus astromech is a no-go; the Emperor is but because he takes 2 slots, you can control very closely where he goes. Would you want a system slot, X7 refit and nien numb as a combined package on a Y-wing, for example? Or Poe Dameron?
Whistler is awesome, but not specifically much more so than R2-D2 or R5-G8. More than a 3-4 point astromech seems excessive.
I'm not sure what I'd recommend for his ability. For R5-G8, I recommended "after you perform an attack that hits, assign an evade token to this ship" - because it pairs well with Wedge, his associated pilot; Wedge shoots early, rarely misses, and his main weakness is his durability.
For whistler, he should probably support Corran's ability in some way - R5-K6 is an obvious pairing for Corran (especially if he has some green dice manipulation from the title) as a 'fire control system' to increase his shootyness, so you don't need that. The converse is that Corran spends every other turn unable to shoot. Since he's not able to shoot, why not push that ability further? Something that's an action that prevents you shooting (which Corran doesn't care about after firing a sustained burst) to let you make good use of the turn. Aside from a custom action to improve defence, the obvious option is SLAM.
What if whistler adds the SLAM action to your action bar? That way, corran can fly in, go dakka dakka, then (on the turn he can't shoot anyway) can SLAM to get the hell out of dodge? That might be too powerful - SLAM-ing at speed 4 twice is insane - but it's worth a thought. You could always add a speed restriction to whistler's card.