It can be done ... my first run was with no prop ... your intake manifold has to be sealed 100% and the throttle body closed.
For my first start I used the original Mazda engine controller - NOT Tracy's EC2.
For what it's worth ...
Jeff

I've got a "club" that I used for test running.  It is drilled for an SAE-1 flange.  I can ship it if you'd like.
On Thursday, May 21, 2020, 9:24:05 AM EDT, Finn Lassen finn.lassen@verizon.net <flyrotary@lancaironline.net> wrote:

1) Without prop any vibration will be from engine and PSRU and can
inspect engine (leaks, etc.) with no fear of prop.
2) With prop less chance of over rev and some cooling air through rads
and oil cooler.
What do you think?
Finn