Why is this so dang hard?

I've had the Ford 400 built to replace Gladys' 351M for a good two years. It's stuffed under the work bench in the shop. Nice, hot 400 that's gonna sound really good and have lots of balls of bottom end torque with that 4" stroke. The 351 runs so good I still cannot bring myself to do it.
How do you pickle your build so it won’t have any problems?