As Kalvin said the DDS would be your best route to go.
I was working on a few older units myself.
But I do have to warn you, judging by you post on this it may be too big of a task for you to handle. Especially not knowing your experience in electronics and old rigs like the 401.
This is not a plug and play modification.
- - dithc this old 'nostalgic' crufty design altogether and build something more modern that uses pll tuning
Under normal conditions I would disagree since I love nostalgic radios myself. but I must agree with free_electron not knowing your skill level. I always encourage folks to learn and repair their own rigs.
Perhaps it would be better to find a buyer for the 401 and purchase a more modern rig that fits your needs