No need to start it. The trans has to come off first. Take the flywheel off too. Just prime the engine and see where it is coming from. With a dry sump you should be able to spin the pulley with a air ratchet or drill or whatever works to get pressure. With oil pressure the oil is flowing and will show where the leak is without the engine running, especially if it is that big of a leak!
I would suspect a galley plug at the back of the block, but who knows. I now check for leaks back there after fighting this a long time ago. Now every engine I assemble gets primed on the engine stand, without the intake on, and with all the rocker assembly installed. The last engine I did had too much oil to the lifters and had a leak out the back pressure relief valve plug. Found both problems right away doing this.
It is very odd though, that you ran it and had no issues on the dyno. Something happened somewhere for some reason between the dyno and install in the car. I am sure you will find it but it does suck... I hate going backwards, but have been there and done that. Just have to get it done. The schedule is a moving target! I do want to see you get some track time before drag week though. Very important to prove out all the systems, do some testing and tuning to get the car's suspension working, I am sure the engine will run hard, but getting it "hooked up" is a job in itself.
