Anyone would've guessed you wrote it

[Newton]

In a classroom, one student (A) to another (B):

A: I'm surprised! How did you know I wrote it on the board? (The writing is not on the board now. Maybe someone erased it, but B had already seen it.)

B1: It's pretty simple. Looking at the handwriting, anyone could've guessed you wrote it. (Guessing in the past)

B2: It's pretty simple. Looking at the handwriting, anyone would've guessed you wrote it. (Guessing in the past)

Are B1 and B2 correct?

[Mr Greg]

Both are correct.

Could suggests that it is possible.

Would suggests that it is as possible.

[Newton]

Thank you, Mr Greg :).

In the same context, the following would also be correct. Am I right?

Anyone could/would guess that you wrote it. (Guessing in the present)