There are a lot of options. Here's one: A few years ago I bought an Epiphone ES335 with the sole purpose of upgrading the electronics. I decided I wanted vintage tone. After a lot of research I bought/installed a BCS Vintage ES335 wiring kit and two Seymoure Duncan Antiquity humbuckers.
Dollar for dollar, this upgrade is one of the best gear investments I have ever made.
http://bcsguitars.com/?page_id=2760
https://www.seymourduncan.com/pickup...-humbucker-set
Side bar: How do you like your OM-40? Is it a good strummer as well as a fingerpicker?