Honestly, considering how very little the ATP has displayed about the rankings in the early 80s (in some years they only displayed one ranking in the year), I wouldn't consider the "weeks records" displayed on Wikipedia, which are all actually made from that source, as really relevant for Lendl and Connors (and also for Borg, McEnroe or Vilas)
... until one day, the ATP displays all of the rankings from that period which they did calculate (according to Slasher, they did calculate rankings on a nearly weekly basis in that period already) but didn't display.
Besides, the rankings in that period, and especially in the 70s for Connors (and Borg and Vilas), were heavily contested,
then I made my own rough estimates as well.
Fed has the clear record for weeks at number 1, can now be considered to be roughly tying Lendl's record for weeks in the top-2 (keeping the number 2 for longer during clay season would not only help Fed to avoid Djokovic in semis but also help him to make a very clear and undeniable mark for that stat),
and now I think his goal should be about staying as long as possible in top-4, as Jimmy Connors did regularly until 34 years old and a few months, and even a few weeks until 36.
Staying in top-4 is also of course very important for slam draws and then to help to prolonge Fed's carreer, that's why it's a very important goal imo to walk on those Connors' prints.
For weeks in top-2 ... Fed has now guaranteed :
- top-2 until the end of Dubai, that is 411 weeks (from further estimations I made, the "reality" for Lendl might be near to 420 then it would be good to do even better for Fed)
- top-3 until the end of Indian Wells as well, that is 500 weeks (from my estimations, both Connors and Lendl might be around 530 weeks)
- top-4 until the end of Miami, that is 512 weeks (Connors around 660)
- top-5 until the end of Monte-Carlo, that is 532 (Connors around 700)
updates : Fed has now guaranteed :
- top-2 until the end of Indian Wells, that is 413 weeks (from further estimations I made, the "reality" for Lendl might be near to 420 then it would be good to do even better for Fed)
- top-3 until the end of Miami, that is 502 weeks (from my estimations, both Connors and Lendl might be around 530 weeks "in reality" even though Wikipedia wrote Connors at nearly 600 weeks)
- top-4 until the end of Madrid, that is 518 weeks (Connors around 660)
- top-5 until the end of Roma, that is 536 (Connors around 700)