This is going to be a bit on the long side and includes some sourcing information.
I never upgraded this sort of stuff on the TR4A I had but did make a number of modifications to my TR6, among them going to -6 (3/8") fuel hoses and tubing from the -5 (5/16"). I believe the fittings at the tank and at the fuel pump are the same size on the TR4/4A/250 and carb versions of the TR6. The hose and tubing from the tank to the fuel pipe are -5 while the runs from the fuel pump to the carbs are -4 (1/4"). Threaded connections at the tank and the fuel pump should all be 1/2"-20, which as luck would have it, is the same thread size and pitch as a -5 AN flare fitting. Like TFB, I used -6 stainless tubing for the long sections of the run along the frame along with a few shorter sections of -6 tubing with braided -6 hose and various AN fittings as the flex hoses to get my fuel lines plumbed. Since there were multiple hard line segments with some complicated clocking orientations for my set up, I did an initial hand bent mock up using soft tubing to get a basic feel for the routing, bend radii (tried to stay at a 3d bend radius) and bend tangent points. While it wasn't the same degree of help for making up the long tubing run along the frame, it still came in handy.
Coming off the fuel tank I used an AN919-7D reducing union, -5 on one end and -6 on the other end. On the -5 side of the fitting, the flare portion was removed leaving the 1/2”-20 section that would screw right into the tank. The bore of the fitting on the -5 side was was increased to match the -6 side of the fitting. The areas where the anodized coating was removed from the fitting were given brush coat of MIL-C-5541 chem film. There are short braided hose assemblies coming off the tank and in the boot where my filter and electric fuel pump are located, as well as coming up into the engine compartment to the carbs and between each of the carbs. The fitting was installed into the threaded boss on the fuel tank using a brushable polysulfide sealant.
You will need an adapter at the stock fuel pump as well if using and this is where it gets a bit trickier for me. I do not have a stock fuel pump handy so I don't know if those AN919 fittings would have sufficient clearance to be used. Operating on the assumption that they would fit, you would need another AN919-7D on the inlet side of the pump along with either another AN919-7D on the outlet if you wanted to run -6 toward the carbs or an AN919-3D (-5 to -4 reducing union) if you wanted to run -4 toward the carbs. Again, this is where the -5 side of the union should have the tapered seat area removed and the bore increased on the -5 side on the AN919-7D unions. If you use one of the AN919-3D unions , you do not want to open up the bore on the -4 side since it would impact the sealing surface.
Properly torqued AN type flare fittings should seal up with no problem but if want a little extra insurance, you could use some Del Seals. These are thin 1xxx series (not sure of which specific alloy) "commercially pure" aluminum in an annealed condition that deform on install. They are primarily used on fittings that have been in service and may have scratches or other small defects. When the seal deforms on installation it fills those small imperfections to help ensure a good seal.
Aircraft Spruce has the basic AN fittings at as good or better price than anyone else. They also sell the Del Seals, the chem film under the Alodine trademark and a number of different versions of the polysulfide sealant. I used the 3M AC-350 A-2 that is a Type A (brushable/pourable) with a two hour working life. It meets AMS-S-8802 (formerly MIL-S-8802) requirements.
Other out fits such as Pegasus Racing, Summit, Jegs, etc have the Aeroquip, Earls or similar for the hose fittings and hose. Pegasus generally has the best prices on the hose fittings. I don’t think any of them have Del Seals, chem film or polysulfide sealants. However, Pegasus does seem to the only one I can think of offhand that carries the Stat-O-Seal and Dowty sealing washers. West Marine carries a line of polysulfide sealants that sounds like it would be semi close to the AMS-S-8802 Type B. It’s from Boat Life brand sold as Life Calk. You can probably find it at any reasonable size boat dealer or boating supply as well. It’s single part, so no mixing required. I do know some people that have used it but I have no direct experience with it.