Beautiful car... lucky guy!

Photos?

With the engine running at idle and warmed up, pulling one spark plug wire at a time may isolate the noise to one cylinder. Pulling the plug wire on a cylinder with a loose rod, wrist pin, or collapsed piston skirt will usually change the "rapping" sound. A persistent miss at one cylinder could point to a stuck valve or broken valve spring.

I had a 1946 Ford that ran well when it chose to run at all. It turned out that it had what appeared to the head of a red harvester ant in the fuel flex line, that acted just like a check valve when it got into the fitting at the fuel pump end of the flex.

The noise could be a stuck valve or broken valve spring. (Or a number of other issues, including, but not limited to: a loose motor mount, dented oil pan or clutch cover, heavy carbon deposits, an issue with the clutch pressure plate, crankshaft rod or main bearing issues, cracked piston, flat cam, and more)
That engine may already be equipped with insert bearings, and an in-chassis overhaul may be possible if the crankshaft is within spec. If the engine is currently in running condition, having an experienced mechanic observe the engine while it's running could give a much clearer picture of its condition and prognosis.

The '39 looks like a good deal for a good car. The 1939 120s retain the 1930s styling and offer an improved cooling system and full-steel body construction with improved body sealing against dust and noise.

Concerning tire pressure:
Owner's manual or shop manual pressures for your specific year and model and body style should apply to any brand tire of the same construction and size as original equipment. I tire pressure specs usually assume a full passenger load, with tire pressure checked cold. Later models with "balloon" tires on drop center rims often had very low tire pressure recommendations, such as 22 PSI for 1937 120 coupes. Adding 10% to that is probably a good idea. Earlier cars with "clincher' type tires and rims had higher pressures specified, usually 50 PSI or more, and it is not safe to reduce the recommended pressure by any significant amount with clincher type tires and rims.

You don't want ANY restriction in your lower radiator hose. It's best to use the pipe arrangement with a smooth, full-diameter bend and to use pipe the same OD as the OD of the radiator and water pump connections. Using the pipe and short lengths of straight radiator hose eliminates any need of an internal spring, and it assures full, unrestricted coolant flow. Stainless, mandrel-bent pipe would be ideal. Or brass. The original pipes were mild steel. The bend, or curve, is a little more than 90 degrees.

Mine does have a flange with single bolt at the block, then the tube extends outward and curves 90 degrees, then straight down to a small bracket on the clutch housing. A picture would be very informative. One of the engine views in the various service and advertising materials in the archive might show it.

That is the slip yoke. It needs to be assembled correctly, or you can get vibration due to incorrect "phasing" of the U-joints. In many cases, the slip yoke spline can be inserted in many ways, but only one is correct to put the front and rear u-joint in the proper relationship to run smoothly. If you clean up the two halves of of the slip yoke assembly and look very carefully, you will may see an arrow and a mark stamped into the metal. The arrow and mark should align.