These have been around for ages and are not worth the cost
If your projector can't do a refresh rate of 120hz you will see a flicker on the image and your old projector won't be bright enough to counteract the dark glasses so you will have a very dim image and I'm sure a lot of cross talk as even the new 3d projectors most models have some crosstalk
FWIW a Lumagen Mini3D Radiance (and I presume the other 3D Radiance models?) can allow a mode where it sends 3D at 30Hz per eye so 1080/60p. However even Lumagen can't make a silk purse out of a sow's ear and they say themselves that it will have bad flicker. I never tried it myself when I had my projector setup so don't know how bad it was.
IMHO 3D is a bit of a compromise on some models that are 'true' 3D so I don't think it's worth it on a 2D model if it's going to flicker that badly. I get major headaches even with proper 3D models...The other issue is finding something worth watching for more than the fact it is 3D: I watched a few of the 3D releases in 2D on my setup and found them pretty awful in terms of how good a film they were: All 3D eye candy and no plot, etc or they were just kid's cartoons, but I guess that's for another thread another day.