Sorry. First link to a DX heat pump was to a diagonal ground-source
using copper tubing at 30 degree off-axis from vertical in 50'
excavations. Will look further.

However, our ducting is sized for the higher heat form a gas furnace.
The first tech advised a heat pump puts out cooler air and therefore
larger ducts are needed, which drives the cost of a heat pump up. Is
this not true?