Your AB test should then be on the Email and not the LP. You would need two versions of the LP, but managed separately.
You solve the problem of giving them the right ebook by setting the form follow up to the TY page that matches the LP. But you would need 2 LP's, 2 TY pages, and 2 assets. Then you can choose to run A/B test on the main LP. You can test this in your email as well by cloning the email and having each email point to the respective asset LP or TY page that matches your email.
LP1 > TY1 > Asset 1
LP2 > TY 2 > Asset 2
A/B test LP1 compared to LP2 and can test your emails the same way.
Email 1 > LP1 > TY1 > Asset 1
Email 2 > LP2 > TY 2 > Asset 2