You won't get a good price on that one. It's a 71 Boss 351. It will cost you about 850, maybe more, if you can find one for sale at all.
Look for a D2ZX-AA. That's a 72 HO and the Service part. It's rare but not worth as much. Probably $350-400.
One comes up every few years but you would be better off buying a Romac as George suggested.
I was just in the right place at the right time to find mine. I had two and they both cost me $125.
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