The 250 damper is a poor design, probably dictated by the bean counters, since the bonded rubber between the hub and the outer rim carries the driving load for the belts, but nobody but a nitpicker with something to sell you would be concerned about a tiny fraction of an inch of belt spacing. In the real world, it's a non-issue. There are hundreds of them in use by people who don't want to pay the outrageous prices the rebuilders want for the original ones. There is also a way to fabricate a balancer using a 6" diameter V8 damper and a 2-sheave pulley for a big block V8. I've made several of them and stovebolters are running them without issue on engines with power steering, air conditioning, and other setups that require two or more belts. Coilover's shop routinely installs serpentine belts on stovebolt sixes, using off the shelf parts and a little common sense.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!