If you want a BY pipe and can find a Dunhill for a decent price, just do it.
Unless it's a very rare and unsmoked model, the value will not move either way much.
I see burned out hunks of crap with replacement stems selling for $200 plus all the time on ebay.
A decent 1976 Dunhill will be a very good pipe. You will not notice a slight difference in quality seeing you've never had any to compare. The 1970s Dunhills are absolutely serviceable pipes to all but the very informed. If it costs in the $250 range, it will sell for that in another decade with much more use. Dunhills of any condition do REALLY well on the resale market. I've never lost money on a Dunhill....and I've bought some real stinkers on ebay. I let the buyers know the condition and the fact I've never smoked it, and they line up with cash in hand....it's a phenomenon.
Check out Marty Pulvers online shop. He is a straight shooter and has Duhills from $50-$1500 at times. Tell him what you're looking for and he may be able to find it.
It's Pulvers Prior Briars or something like that....just Google Marty Pulvers...hes a legend.