It's a 51 Plymouth that has it's original 218. However, and this is where you are remembering, I have the 230 out of a 52 Dodge I am hopping up to put in her.

Yes, there are performance parts for the flat head 6, specifically the 23 inch version. Which is prbably what is in your truck, If you can tell me the engine number ( stamped on a machined pad the front of the driver's side of the block, just below the deck surface) I will tell you what you have.

I have, new production,the following

High compression aluminum head Mopar Vintage speed is the source
Dual 1bbl intake, it's a Thickstun intake made by the original designer's son, Ebay, he runs a batch off every so often, though I have not seen one recently. https://www.ebay.com/sch/i.html?ssPageName=&_ssn=eastcheam842
Split cast iron exhaust manifolds (basically Fenton copies). This was from Langdon's, but he's no longer in the game. He also made an HEI based distributor.

No one makes new cams, but several companies can put a performance regrind on yours.

You can use a slant six distributor and your existing points one to make an electronic ignition distributor. Modern production points suck horribly. https://www.jalopyjournal.com/forum/threads/mopar-flathead-6-distributor-upgrade-48-desoto.653565/

Vintage Power wagons has stock type replacement engine parts, but is also one of the performance cam sources.

On facebook, The Freewheeling Tony Smith is a machinist that specializes in the Mopar flatheads and sells some parts, as well as a very helpful fellow.

For general truck parts of that era https://dcmclassics.com/

I can help on the engine performance questions, but the truck specific stuff, not so much,

Anyway, here's the build thread on my 51 https://board.moparts.org/ubbthreads/ubbthreads.php/topics/2789776/1.html

A shot of the EFI set up on the bench