Selling car to a friend using finance?

[Babw]

I have a bit of a dilemma.

I'm selling my E46 M3 to make space for a GTR. A good friend has made clear his intentions to buy it but he can't come up with the all of the capital.

Is there any sensible way to arrange monthly payments without resorting to finance? A simple contract of some sort?

At the moment I don't need the funds from the M3 sale for purchasing the GTR but I'd like to get the amount settled with 12-18 months max.

Appreciate the help.

[Babw]

I'm completely aware of the pitfalls and wouldn't have put up this post if I felt comfortable.

I just want to make sure I had explored all possible avenues but really the bank loan aspect with the current low finance rates seems to be the answer for him.