A lot of this depends on which version of G1 you want to go with. Because the characters vary wildly between them.
Like some versions, Grimlock is a former decepticon with an honor streak. One version of Shockwave is fanatical as frak, while the rest would and have beaten megatron to a pulp at the drop of a hat.
Then there's also designs. Optimus, Megatron, and Scorponok aren't the only G1 homages in early Beast Wars. (And all three of those have beats to the originals in ways most people miss) Cheetor is an homage to the Nissan design. I mean, he turns the Prowl design into a cat, beat for beat. Terrorsaur is the standard seeker design (the tail becoming the nosecone-like chest, his head has a stylized seeker look, and the upside down wings brings it home). Dinobot has several dinobot beats. I'm pretty sure he was originally intended to be an update of Grimlock at some point (which was eventually realized anyway). I'm pretty sure Waspinator is an homage to a G1 design, but I can't quite peg down whom. (Unlike most, whom only associate him as seeker because of the show putting starscream's ghost in him, I don't see any seeker styling in his original toy)
So, talking about roles in the show... Cheetor is a hybrid of Bumblebee, Bluestreak and Hotrod. Rhinox is definitely Ratchet. Scorponok and Inferno are like Sunbow Soundwave and Shockwave, only stupid. Tarantulas is like every other Shockwave, only insane. Dinobot parallels DW Grimlock. Terrorsaur is definitely Starscream. I don't think the others really have any G1 parallels. That includes Optimus and Megatron.
When the characters got the beast modes - what if they didn't get mode to match names. Or did they alter their names? So if Rhinox got the rat form? But when you watch the pilot it looks like they rename themselves?