Hey man, I'm currently building a 230 for a friends 51 Dodge pickup. He's going to have about 2grand in it complete running. What follows is basically what I did for him.
If I were you I'd build the engine you have in your Plymino now. If it's a 218, find a 230 crank and rods and it becomes a 230. VPW sells them new, but they can be had for much less. Bore the engine to whatever ovesize you feel comfortable with, I go .060 as a rule. The best money you will spend is on balancing the moving bits, worth every penny. Install a high volume oil pump from VPW. You can use your old cam if it's ok, or run a new one, stock is fine.
I have had all the high dollar aluminum heads, intake, headers etc. They are really great, nothing wrong with them, very neat, but not strictly necessary. I sold mine to pay for my complete engine overhaul! I would run the stock head, maybe have it trimmed .050, and deck the block .010. George Asche takes 100K off of his and he's the master. Install head studs, forget head bolts they are the cause of blown gaskets.
Get a 2bbl carb kit and HEI ignition from Tom Langdon at Stovebolt. You will get as much intake as you would from duals without all the balancing headaches and water tubes. The HEI eliminates any ignition problems, period. Convert to 12 volts and run an alternator.
Find yourself a second exhaust manifold and cut the flange off flush with the manifold. Cut a second exit hole in the manifold you will run on your truck. Have the second flange brazed on and you've got dual exhausts for around $30. You can braze the heat riser flap shut if you want true duals, but you don't need to. The idea is to increase exhaust flow, not necessarily to split the exhaust, either way is fine. The old time flathead racers added a second dump and ran open pipes.
If you have a harmonic balancer send it to Damper Dudes and get it redone. Get a new water pump, water tube, hoses, wires, etc. Anybody can assemble the engine if they take their time, read the manuals and double check themselves at every step of the way.
Built this way your flathead will have plenty of power for the street, should be very dependable and require little attention.
Anybody who offers to build you a flathead for $3500, even in California is probably a politician, a thief or both!!!! or maybe just an actor................
