I've done a bit of looking; and I came up with this It's a string gauge/tension calculator. Enter the gauge and the note the string is tuned to, and it will calculate how much strain you are putting on the guitar.
Gibson archtop tenors used the same bodies as the six-string versions, but with a four string neck. I'm guessing that yours is one of the tenor versions of the L7, which was a big jazz guitar built to take enormously heavy strings. (This was to produce the volume needed to play unamplified with jazz bands)Legend has it that some of the old jazz guitarists played bottom E-strings that were .075" ! Strings for real men! If the guitar is in good condition and has no bracing issues, I can't see any reason why it wouldn't handle four strings tuned to the top four strings of a 'standard' guitar. Wouldn't be my choice though; I think the 'voice' of the tenor needs a tuning in fifths, preferably CGDA...but I would say that, I'm a mandolin player and I like fifths! Good luck with your choices.
Tim