My only advice would be to take 5, stand at a distance and just think with your head, not your heart. If you really want a Sandman then you'll never build what you described for $25k, in fact you'd never build a replica as you describe for that. But if you are eyeing it with thoughts of investment i'd walk away. Like GTR's and SLR's the Sandman is a niche car, not a premium performance and asking prices are over the top at present. If you are thinking half enjoy, and half investment i'd hold out for a 5.0L example in similar condition.
Just my thoughts anyway.