If Whitworth retires, I would prefer that the Rams spend that freed up cap space - plus more, if needed - to go sign a big money LT. Armstead would do nicely, for example.
LT is one position you do not play around at. Big Whit is an absolutely elite LT, even at age 40. I believe he was the highest-graded pass blocking offensive lineman in the NFL this season. He can pass block to great effect, as well. The Rams' ability to pass block is, IMO, the top reason why they are Super Bowl champions at present. Stafford was rarely under duress when compared to other playoff QBs. We need to retain that level of excellence. Especially with McVay being pass-happy and the Rams' offensive playmakers being concentrated in the QB and WR positions.
I do not trust Noteboom to stay healthy for a full season.
Jackson looked good in limit reps, but is too untested to roll with for a team as Super Bowl ready as the Rams.
Stafford already has an extensive injury history and is starting to get older. It is imperative to protect his blindside.
The Rams are primed to run it back. Rolling with what you have in house, at a position as important as LT, when your in-house options are somewhat unknown quantities, is something I would expect from a re-building team, or a team on the cusp of a playoff spot, or even a Super Bowl dark-horse. Not a pre-season favourite to win it all. Unlike other positions in the NFL, rest assured there will be no mid-season replacements available if the in-house guys prove lacking, because other teams don't let capable LTs shake loose mid-year.
I am cautiously optimistic the Rams will see it my way. They generally seem to de-value lineman in the draft, using only mid to late round picks on OL, to groom for future usage, as they coach up whoever they have in house to man the ship in starting roles.
HOWEVER, they did not hesitate to open up the wallet for Havenstein at RT, or at LT for Big Whit, who I believe was McVay's first free agent signing.
It seems the Rams place grate value on their bookends, indeed, even if they somewhat ignore the interior - to the point that the Rams often draft tackles to play guard, which I suspect is in no small part motivated to build their tackle depth in the event injuries pile up at the position.