I put Grado SR-125drivers in a beyer shell.
Its an interesting combination, with some parts of the DT-770 sound staying, and some parts of the SR-125. To agree with punisher, there is no lack of bass. Not QUITE as much as a DT-770 proper, but more than the sr-125 had stock! All in All I do like it, but would not really recommend it unless you have a basket-case DT-770, and dont mind the risk of totally destroying a set of grados.
FWIW, My shell was at one time a 600-ohm DT-770. It sounds pretty good with only a 1/2" cube of foam from a pelican case for damping. The DT-770 is not a sealed headphone, there is also a hidden port.
First and foremost: not all beyer drivers are the same size. PWNED! The 80-ohm drivers are FAR too large unless you want to go all jerry-rigged and glue the grado drivers in. I have never seen a 250-ohm driver so I cant say.
If you have an enclosure that you think will fit them:
If necessary, carefully remove the beyer driver from its "mount." It probably requires removing a little hot-glue and stuff. The stock grado driver in my headphone fit in with acceptably little play, while using all of the stock beyer mounting tabs.
You remove the grado driver ENTIRELY from the tube. this probably requires cutting a couple slots in the tube and breaking it off.
Then you will see an obvious step where the "protective mesh" that goes against your ear on the driver attaches to the actual driver. I used a dremmell and CAREFULLY cut the rim of this in about 6 or 8 spots equally spaced around the driver. Do not cut too deeply into the actual driver!
Remove the cover. My memory places this somewhere breaking the cover into little pieces, and peeling it off. Did I mention you have a good chance of destroying your headphones? Now is a good time to break off a chunk of plastic and simultaneously poke a hole in your driver
dont do that.
If you were lucky&careful enough to successfully get the grado driver "naked" without screwing up the speaker, and planned well for the size of the beyer shell, the grado drivers will drop into the housing.