Ironically the best (under $2000) choice for B&W will be a business DLP. Not the w1070, not even the 131xe/hd25e, but a full-blown, rgbcyw colorwheel business PJ with brilliantcolor turned all the way up.
The rgbcyw wheel with a low power lamp and high claimed brightness means most of the wheel will already be dedicated to white-brightness just like you want..with NO modification.
I'm not sure how many full 1080p B&W films there are, so choose your resolution with that in mind as well as the fact that this will be a B&W projector that will do a much worse job at colored films.
Look at projectorcentral.com and search all DLP, with brightness. claimed 3000+ which will guarantee rgbcyw colorwheels. If 720p is good enough for resolution, I'd suggest the Benq mw663 or the cheaper mw519.
When looking at individual models, expect lamp wattage to be at or under 210watts..usually 190-210.
Also, I've heard plenty of stories about old dlps finally giving out or getting dropped and still working with broken colorwheel, so your idea seems sound enough to try with something cheap enough to afford possibly breaking. If nothing else, get a cheap 3000+ lumen DLP and see if it works fine as-is. If not, it's a cheaper piece to experiment on and it seems like the plan should work.
Last edited by Ftoast; 07-24-2014 at 12:41 AM.