[Steve DeRosa]

Some options:

• If you're happy with your '53 L-50, Krivo's Micro-Stealth pickup is made specifically for low-clearance guitars like yours - not cheap at $200, but the reviews are excellent:
  
  https://www.krivopickups.com/store/p...zz_Guitar.html
  
  
• Lollar offers a custom-order McCarty-style pickguard, copied from the Gibson originals and designed to fit any Gibson archtop:
  
  https://www.lollarguitars.com/blog/2...rchtop-guitar/
  
  
• Several companies produce either under-base or saddle-mounted bridge transducer pickups, designed to offer a more "acoustic" sound without modifications to either the guitar or pickguard; a few examples:
  
  https://www.pickup.world/product/vin...rchtop-guitar/
  https://www.fishman.com/portfolio/ar...guitar-pickup/
  https://kksound.com/products/definity.php
  
  
• Sometimes nothing will scratch the itch like a new guitar, and if you can't afford a genuine "Mother Maybelle" L-5 the Loar LH-700 is a near-exact replica at around $1500; be advised that it's period-accurate in all respects - including the classic midrangey prewar tone you say you're after (IME the 16" Eastmans are sweeter-sounding and lack the "cut" of a vintage guitar) - but if you're accustomed to a slimmer postwar neck the 1-3/4" thick-V profile might be more than a bit daunting (the only reason I don't own one right now). You'll also need to make sure you get a "good" one - I'm not familiar with recent examples but earlier ones had neck-set issues, that caused problems ranging from poor tone (FYI neck geometry is extremely important - far more so than a typical flattop) to complete unplayability - but the best of them can punch well above their weight:
  
  https://www.theloar.com/p/lh-700-vs
  
  
• Finally, here's a reasonably-priced postwar L-4 already equipped with a professionally-installed pickup:
  
  https://www.archtop.com/ac_48L4_920.html

Good luck...