Which of the lineal heavyweight champions would Sam Langford have beaten?

I don't believe he was 218.

Maybe 218 was the number he cut his monthly doughnut supply down to.

 

If you want something of a modern visual for Langford against a tall super heavyweight, check out Foreman-Qawi, where Ike actually manages to win some rounds. We also know what Langford-Leon Spinks would look like thanks to the Buzzsaw.

Sam was an inch taller than Dwight, with an inch more reach. (Both men had freakishly long wingspans for their height, although much of that is collarbone length, as was the case with Liston.)

For the 20 rounds of Jeannette X in Paris, Langford was a solidly well conditioned and granite chinned 200 pound brick outhouse. But I can't see him taking the title by knocking out Willard (which he'd have to do under the rule set certain to be in place for such a challenge), Johnson in a rematch, or Jeffries (who was left arm impaired in the Sharkey rematch, hence all the damage inflicted in Sailor Tom by Jeff's right hand, on the left side of the challenger's face and body). In real time, Sam's only clear opportunity to become a champion was at the expense of Burns late in this fellow Canadian's reign, and I wouldn't put money on that outcome after watching how the rugged Tommy starched the favored Squires in one. (I don't think Langford was quite ready for Hart, or Burns through most of Tommy's time as champion.)

Reigning era Patterson was extremely vulnerable. Sam outreached Marciano as well as Floyd, and garnered two knockout wins past the championship distance. Frazier openly admitted that he didn't like taking on shorter opponents. For both Rocky and Joe, Langford could be a major headache. Schmeling was starched in one by Welsh LHW Gypsey Daniels in their rematch, so it's not impossible for Sam to turn the trick. Max would need to apply even more than usual vigilance here. A much past it and out of shape Walker did have his moments with Schmeling, and Mickey had five inches less of reach than the Nova Scotia native.

As erratic and volatile as Sharkey was, he could be very susceptible. Even at his best, this fellow transplanted Bostonian didn't have the punch to dent Langford.

Charles and Walcott would need to be at their best, as Sam had the power to drop and stop either. Here, we're clearly in masterclass territory.

Where Liston is concerned, the 200 pound Langford is big enough, durable enough, and tenacious enough to break Sonny's will. Sam would have been far smarter dealing with Liston than Patterson was. Slip the jab, counter, clinch, move, bide time, then drown the bigger man in the deep end of the pool. Langford weighed the same as Leotis Martin, was more solidly built, carried a bigger punch, and had a better chin. Sam by late knockout.

Jeannette showed me enough against Langford to convince me that Tunney and Corbett would have decisioned him. Both were taller than Jeanette, who did have some success using his height and speed to box from longer range.

Max Baer would have been at huge disadvantages in speed and accuracy. Nor did he share the same commitment post Campbell as prime Sam. Being tall and durable as he is though, Langford settles for a decision. The 5'9' Galento did have some moments with Maxie, even getting his short jab through.

Tyson had a terrific uppercut, but a style primarily geared for taller opponents. Sam's heart, stamina and durability creates interesting issues for Mike. Again, Langford would have a slight reach edge, the lower center of gravity, and the prime for prime weight disparity could be less than ten pounds if records are accurate.

 

Douglas was undisputed champion of the world, no less.
But as I've already stated, journeyman and contender aren't mutually exclusive terms.