Really too long, especially if you don't have an extension bed, extension bellows and mid frame for your Sinar
Artars, I could never tell the difference between Apo and RD in final print quality, are very good lenses, but a 210mm Xenar should be easy to find and if you want a softer effect try a 250mm Rodenstock Imagon, which by purest coincidence I have here in my safe
However, the Imagon has too much softness for my taste, it was designed that way and mine is complete in original box with all the colanders etc for Au$640 plus postage - I should really put this on the classified section or I will be in trouble
Before you consider an Imagon look them up on the Wise and Wonderful Web and seriously consider the work you plan and if it will be suitable - I did this, but never actually used it apart from a food book photo job with frothy deserts and cakes - For that it was superb and earned its keep very quickly
For a sharp lens in 240mm I have a now unused Apo-Ronar in an ancient Copal shutter which was used for artwork documentation for publication - Perhaps a Au$1 per millimeter plus postage, but I am open on that - Or a 210mm Symmar S in more recent Copal shutter that is too new and "bitey" for my taste - Perhaps Au$1.50 per millimeter plus postage
However, think before you spend your money - Also, tipping other people to eBay items may not be in your best interest if you don't want other APUSists bidding against you