Try it with the engine mount off the Firewall
I just did this on Monday evening. It worked beautifully. I am still on a high as a result.
I had intended to gather a posse to do this with me but I got to the point where the firewall was ready and it was still too early to quit for the day. I was conscious of a lot of people who have chosen to attach the engine to the mount first and then bolt the assembly to the firewall. So I though "I'll just give it a try and stop at the first sign of trouble" 45 minutes later, (including clean-up time) there it was.
This method gives unimpeded access so that you can sight through the holes and see exactly what movement is needed to get it lined up.
I followed the order of bolts quoted in the
illustrated guide. I found that fully tightening each bolt helped to bring the next one close to its final position but it was necessary to slack it off a bit to give some wriggle room. The next bolt could then be angled to get one thread onto the lip of the hole in the engine block. From there I turned the bolt to 'screw' it fully into place, as recommended in the guide (no hammering). The threads help to pull the bolt through the hole to a point where you can easily get a washer and nut on it. The bolt obviously straightens up as it goes through the hole and brings the mount into alignment.
I also used one of my temporary wing bolts that was ground to a bullet shape as a drift pin but this was mainly to get the rubbers in line. You can't do much pushing and pulling with the engine hanging like that but you can still lever the mount against the engine. I must confess to trying that on the third bolt but it probably wasn't necessary (protect the powder coating if you do that).
In case anybody notices, this is a pre-loved engine, which accounts for it's slightly less-than-pristine appearance (O-320 E2A, 274 hours since rebuild to new specs by Mattituck - taken from a retired Cherokee with an expired CofA.)