From my recollection, I'm assuming that you're talking about the "gritty-ness" of the beats that the East is(was RIP), known for, right? Like the hissing-due-to-sampling-everything-on-the-beat kind of ruggedness, right?
If this is the case to be honest, you won't find much luck trying to make a, say, keyboard-based beat sound like (for example) "Juicy" from Biggie. Reason being: there's nothing like sampling. People think that sampling is stealing. However, there's a vibe that sampling gives your beats if you do so, something that no plug-in or sound effect can emulate. I'm talking sampling from drums, too. (How do you think old Hip Hop heads got their sounds back in the day if they didn't have an 808?)
Example: I had a kid come to me with a piano-lead beat he made on
a Roland MC909 drum/synth machine, and he wanted me to make it sound like it was sampled off an old record. Though I made it sound close and he was satisfied, it was nothing compared to if he actually sampled those sounds from records. Why? Take into consideration that keyboard sounds are "immitation" sounds of the original sound they're tryin to emulate. Also, when sampling, it has more of a smooth feel since the majority of records from back in the day were recorded analog from people using actual instruments... so things like "quantizing", "sequencing" and even 44.1k 24bit sound was not only unheard of during the time but THROUGH time the records lose their quality. Let's not get into the "cutting" phase of what it does to the "east coast" sound, cuz that'll be plenty more paragraphs.
Overall, if your beats are created and based around keyboard sounds and/or contemporary sounds like what you hear on the radio, it'll be a process to make them sound like the original East Coast sound. As far as artistically, that's on you and your music, cuz you can't "engineer" and morph a Miami Bass beat into an old East Coast beat unless it's done artistically; but technically you can't make it happen.
I would suggest to try and get some plug ins that emulate old sounds, etc. It's all about what your ear hears and wants. Most recording/editing programs have multiple effects on them that you can mess with to make your keyboard sounds different, both quality wise and/or artistically. I love keyboard-based beats where the producer basically PLAYED his own effects into the beat and created his own sound.
Hope that helped.