The MA-505 is a wonderful tonearm utilizing dynamic suspension. Assuming that the suspension is in good condition your tonearm will work well with a wide variety of cartridges, including the DL-103. One word of advice: more expensive doesn't necessarily mean better. Just different. The phono cartridge needs to be compatible with the ability of your entire system to reproduce sound. For example, many cartridges are amazingly detailed. Can your other components do an expensive, detailed cartridge justice? Maybe yes.
Really, it's about what you like in a cartridge. The DL-103 is a high output MC cartridge that will work well with most standard 47 ohm (MM) phono stages. You know what it sounds like so I don't need to describe it to you. IMO the MA-101 tonearm works best with a midweight, middle compliance cartridge. If you want more warmth and detail in an MC cartridge I might recommend the Ortofon 2M Bronze. The Grado Platinum or Statement series would also work well. If you wanted to try an MC cartridge I would suggest any of the Hana cartridges.
One last thing: the BL-101 turntable was considered a good turntable in it's day (1980s) but it's a little noisy and quite resonant by today's standards. I'm not saying you don't/won't like it. But you can only wring so much sound out of that deck. Trust me. If you want to try an expensive cartridge I would suggest mounting that tonearm on a better deck. If you want to stay vintage you might look for either a Luxman PD-441 or PD-131. Most modern decks will require drilling or retrofitting to take the 27mm mounting hole required for the MA-505. It's a bit of a PITA but it's worth it, if your tonearm is in excellent condition.