It might be helpful in determining cost if you were to examine some of the detailed cost sheets others have provided for their specific builds. A lot of that is for components, but good machine shop experience can get pricey
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I used to think one can build an inexpensive truck-based 409 engine for less than $4K (I couldn't pull it off!). The basis would be a truck block with 333 heads, an OK intake/carb setup, standard crank, new rods and pistons, etc.
Now I am thinking one can build an inexpensive truck-based 348 for less than $2K. Pretty sure I'm gonna find out otherwise
Just think about the cost to "rehabilitate" that 6x2 set up you have: $30 per carb for the kits, $200 for linkage, $xxx for fuel delivery, etc. If you paid a professional to restore those carbs and intake you'd be getting close to the cost to build my "budget 348"
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Good luck in your decision making, let us know if you need any details.
Best,
TomK