Bringing this back from the dead to answer the question - you will need
(4) M12 x 1.75 80mm - but keep in mind the length all depends on your engine stand as some have longer holes to go through.
I also use a washer on engine side as well as engine stand side.
I have mine attached @ all 4 corners
This is confirmed on Red & Black tops - not sure on S15 SRs
Now in the last pic - this would be the "best" motor building stand as the stand will not get in the way of you micing out your main journals etc. As long a you got a spare motor mount bracket and somone to weld it for you your good.