You'd need to make a lot of changes to make the 140 wheels fit the amazon. They have a different bolt-circle.

Few parts are compatible between the 120 and 140 (aside from the engine and gearbox).

The 1800 has a lot in common with a 120 (same basic chassis) but only the 1967+ 120s are an all-wheel direct swap with the late 1800s. That is, you can install the hubs, calipers, and rear axle from a later 1800 into a later 120 with no issues and this would let you use the newer wheels, but a 65 uses a different type of axle, so you would have a hard time upgrading the rear end to use newer wheels. Disk brake 120 front wheel hubs are direct swap with all 1800 front wheels.

Yes, you just take the whole booster assembly and stand off the 140's firewall, remove the "foot" flange from the stand and have a custom triangle-shaped foot cut and welded on. The booster will bolt directly to the 120 pedal box and you just have to adjust the pushrod to fit the pedal.

Voila "modern" booster brakes and still 100% volvo. It is by far the easiest way to get a modern brake setup on a 120.

By the way, if you are junking a 140, I'm looking for the upper steering column so that I can install a locking ignition switch. Only the 1969-1970 120s and the early 140s use that setup.