Is there an easy way for me to just trim what I already have, attach new eyes, etc?
That would be my approach.
If you know how much you want to shorten them, you could take them to any marine place and have new fittings put on.
As for the correct length, there are a lot of factors... (not the least being the geometry of the boat - esp. the height of the mast-step relative to the plank)
Cheers,
Geoff S.