Newby with a question - Castor angle

[Dazza]

Hi Guys
Ive got a '29 Model A with a bit of a handling issue.
Its been like it since i got it 18mths ago.
She tracks and pulls up beautifully.
But digs in going around corners and if i hit a bump she'll change lanes on me, but carries on straight.
Now thats fine on the dirt track, but scares anyone man enough to brave a ride in the co-pilots seat haha.
Ive had it on crossplys, ive had it on radials.
All the joints are tight and good.
One thing i have noticed is that the king pins have a slightly negitive castor angle (leaning forward)
I dont see a way to alter this so assume its correct???
Unless the front is (and can be) in back to front???
Any help much appreciated
Thanks
Daz