Yeah as Cyberknight said I may have some insight to this, I rode there and back a few years ago, and, potentially doing it again this year, but in half the time!
To be honest it depends on what you want I guess, back country lanes where you can pootle along or a bigger road where you can just get your head down.
Picking the route up where I rode above Leicester it would of gone: Upper Broughton, Long Clawson, Croxton Kerrial, Great Ponton,
Boothy Pagnell, Ingoldsby, Folkingham, Billingborough, Pointon, Gosberton, Sutterton, Kirkton, Wyberton, Boston, Butterwick, Wrangle, Friskney, Wainfleet All-Saints, Croft, Skegness. That was my roughly 2012 route missing out the first X amount of miles.
If I do it this year it will be the A607 and then the A52 - job done...