Whoever the famous Eric Jackson is, I assure you I'm not him... And two sons, no daughters.
Casting V8 manifolds will be a huge job- stepped parting lines, elaborate cores and core boxes, gating and venting will be critical to get good fill and feeding. Fixturing for machining will be involved also. Best of luck, you're braver than I am.
Lost foam casting is common, it uses the same basic approach as investment casting. The pattern is made of sacrificial foam, dipped in a ceramic slurry to create a hard candy shell, the foam is vapourized by the heat of the molten metal. Investment casting uses wax for the pattern, often lots of small parts on a christmas tree- like sprue. The wax is vapourized by the metal, the ceramic shell contains the metal until it solidifies, shell breaks away to leave parts. Lots of jewellry is investment cast.
For onesy- twosies, I gotta believe sand casting is the best route. IIRC, .004 per inch is the shrink rule of thumb for iron.
