Major leak issue with new engine install, need any and all help guys

[UATahoe]

Ok, finished up installing the 383 in my 87. Started it up 3 times now in the garage. Hasn't been driven. Would let it idle and get up to temp and then shut it down. Checked it over for leaks and all was well. Decided to back it out of the garage and let it run again this evening. My driveway is on a pretty good incline to get into the garage. Let it run up to 180 degrees and then shutter down. Once I turned it off some type of fluid was leaking very steadily down the Flexplate. Looked like it could have possibly been coming from the rear seal. A picture of the fluid is below. What is puzzling is it seems to have a very strong gas smell to it. Didn't want to start it up again so got a lot of help to push it back in to the garage. Once it was on level ground, the leak quit immediately. I am totally puzzled on this one and fearing the worst here. Have no idea what could be going on.
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