Churches seem to have a common theme of having initially installed a high quality projector, with a very long throw distance, then not budgeting appropriately for a replacement.
You aren't going to replace an aging quality unit 'on the cheap'. It's going to cost several thousand dollars at the very least, which is likely less than what originally may have needed to have been spent.
With only 7' of screen width (about half of what would be recommended by the way), you need to use a lens which has incredibly long throw, and it makes sense to re-use what you have.
But, most manufacturers use lenses which are specifically designed for the projector it is attached to.
So, I would try to call either Navitar/Buhl or I would call Eiki and see if you can get any lens compatibility specifications for that lens, or see if it uses a 'standard' bayonet type mount. If it can work with other projectors from Eiki, or others, then I would start looking at those models.
This model has similar features to what you are replacing and allows for interchangeable lenses. But, none of the listed lenses match up to what the model you had used. Yet, what you have as a lens doesn't match up with the standard model numbers for the projector you had either.
So, there is a chance you can make it work with the lens you have, but you still should expect several thousand to be spent on a projector which allows for interchangeable lenses and can support ultra long throw.
Getting away from that lens, and going to something new, this list provides all the sub-$5,000 options out there.http://www.projectorcentral.com/projectors.cfm?g=1&hide=0&st=1&mfg=&p=500&p=5000&w=&r=&br=&ll=<g=&t=&db=&dt=&c=&ar=&dvi=&wr=&pjl=&pjw=&pjh=&td=50&i=w&is=84&oop=1&sort=%24&sz=15
The NEC at the top of the list seems like a very good deal at about $1,600...http://www.focusedtechnology.com/nec-np-pa600x-projector.html
Unfortunately, the lens is another $2,300...http://www.focusedtechnology.com/nec-np15zl.html
This is a situation, where I might buy the projector, see if the lens you have fits it, then buy the lens from somewhere else (closer to $2,000 elsewhere) if the lens you have doesn't work.
Nikon, Canon, Minolta, etc. all use different lenses. Some of those brands have different mounts within their camera lines. So, it's not a shock at all that there is so little standard within the projector manufacturers.
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