Great start.
If you are not already signed up over at the P15-D24 site
http://www430.pair.com/p15d24/mopar_forum/index.php?referrerid=1152 I would suggest you do. There is a ton of info over there on these old Mopars.
One other suggestion is to look for an R10 Overdrive from a mid to late 50's Plymouth or Dodge. It is a direct bolt in as long as you do not get one from a fluid drive model and you retain your column shift. Once in just add a few wires for the solenoid/govenor and you are ready to go. The OD will let you comfortable cruise at 65-70. Another option to get an OD is to go with a T5 from an S10. Paul Curtis
https://home.comcast.net/~pjplymouth/t5.html sells an adaptor for the T5 to Mopar flathead. Lastly is to go with a 90 or so Dakota or early 70's B-Body 8 3/4 rear. They are basically a bolt in with relocation of the spring perches. Your stock rear will be a 3.90:1 or 4.10:1 gear which will limit your ability to cruise on the highway, the OD or rear swap will help greatly.
I went with the R10 and it is probably the single best mod I have made with the possible exception of the front disc brakes.
A stock rebuild of the front suspension with a couple of mods will be more than adequate. Olddaddy
http://rustyhope.com/ sells what is basically a bolt on disc brake kit. It requires you to drill/tap the three spindle mounting holes to a larger size then just bolt everything on. Lastly is a relocation of the top shock mounts to the frame rather than the upper control arm which greatly improves the ride.
Here are a few photos of my 48 coupe.
Here is a video of my old 218 running prior to the swap to my new 230 with the aluminum head. Rest of the goodies were swapped over to the 230. These things sound great with split exhaust. Mine is running through dual 2 1/4 inch pipes with short 14 inch no name turbo style mufflers.
http://www.youtube.com/watch?v=AxfKQ4KMM9s
There are starting to be a few suppliers with parts for the flathead Mopars.
Edgy Speed Shop -
http://edgyspeedshop.com/ - Finned aluminum heads, dual intake, reground cams
Langdon's Stovebolts -
http://stoveboltengineco.com/ - Dual intake, Cast Iron Fenton repop headers, Mini HEI distributors
You can also find some vintage speed parts on Ebay from time to time but they tend to be a little spendy.
Good luck with your build and I am glad to see you stick with the flathead. If I can help any way let me know.