I had first series old SN blower that I installed on my former 66 Shelby clone. It had been removed from a friends real Shelby and I purchased it about 8 yrs ago for $500. I installed it about 1.5 yrs ago and it did not work well at all. Boost was under 5lbs and the air charge was too hot that it actually made less overall power in the upper RPM bands.
I listed it on ebay about one year ago and it sold for $2800. Albeit, it was fully complete with all brackets and carb housing. It was a nice item but only for show. You are better off buying the new stuff.