Keep checking the fluid until you get it full. You can pull one of the trans cooler hoses and see if it's pumping fluid if it doesnt engage once it's full of fluid. Hopefully you didn't break the front pump installing the engine. It happens sometimes that you think you had the convertor lined up correctly but it was sticking out too far. When you tighten the transmission bolts up to draw the engine up to the bell housing you break the front pump.

The spacer and convertor extension are 4L60e parts.