Log in over at the P15-D24 Site
Homepage there is a lot of info there on the flathead Mopars.
Langdon's Stovebolts
Langdon's Stovebolt Engine Co. | Specializing in GM 6 Cylinder High Performance Parts he has dual carb intakes, cast iron headers.
Edgy Speed Shop
Edgy Speed Shop he has dual carb intake, finned aluminum head, and he regrinds cams.
If you don't want stuff now, you can find vintage parts on EBay from time to time but they usually go for steep prices.
A fairly cheap way to increase performance is to have your head milled. Your stock head is right around 7.0 compression ratio, if you mill it 0.050 you will bump your ratio to around 7.7. Just make sure that you use some clay on top of valves first to determine how much room you have before getting it milled. Some of these old heads and/or blocks have been milled in the past to flaten them during rebuild. Some on the P15-D24 forum have gone as much as .100 combined on the head and deck of the block when they were still factory spec.
Look for a Borg Warner R10 OD transmission they were in early 50's model Dodges and then in the Plymouths starting around 53. It is a direct bolt in swap for the stock 3 speed. Then just add a few wires for the electrical controls and you are good to go. I have one in my 48 Plymouth and it made it a completely different car on the highway.
Paul Curtis
https://home.comcast.net/~pjplymouth/ has an adaptor to put an S10 T5 behind the flathead.
Here is the 230 in my 48 Plymouth coupe. With the R10 OD behind it I can cruise at 70 all day long.
