[Ronnieroadster]

HopRod welcome to the Barn.
Since I have dabbled a bunch in a number of fast straight line flathead powered rails heres my thoughts.
To achieve some type of decent MPH and ET your going to need RPM and horsepower. Unless the rail is extremely light less than 1000 pounds which realistically is not possible being only multi carb your extremely limited on what you can achieve.
Being in North Carolina most tracks you will run on I think will be 1/8 mile. So first off your going to need a rear gear thats well north of 411. My choice of power adder to the flathead would be a 471 GMC blower with a decent size Holley dual feed four barrel carb on top. Running a blower drive ration around 12 percent under. You could use a decent stroker crankshaft but most are offshore quality or stay with the 3-3/4 Ford crankshaft which I have found o be extremely strong for most blower combinations. However the rods I would use would be aluminum and the pistons forged light weight possibly from Ross the bore at least 3- 5/16. This would give you a 258 cube combination with the blower the crankshaft HP will be over 300 easily. Now if this is something that sounds good for you I can help you with every part needed for the blower combination. I have plenty of 471 blowers and the intakes for the Flathead in stock and can easily assemble the required drive assembly complete. Theres lots more I could write but for now lets see where this goes. I would suggest one more thing pay attention to information you get. Your looking for ideas and input from the very few individuals here on the barn who actually have the experience needed to give you guidance
Ronnieroadster