The transmissions you refer to have a chevy bell pattern which is the same as a 4L80E. The adapters are rather cheap to go from a BOP engine bell pattern engine, to a chevy bell pattern transmission. No need to re-invent the wheel.
Link to Jegs:
https://www.jegs.com/i/JEGS/555/60172/10002/-1
Many people don't know that the 2 lowest bolts, and the pilot dowel locations on chevy and BOP patterns are in exactly the same position. The upper bolts are the only ones that don't match up. The adapter I linked to matches the upper holes up, the 2 lower holes already match up and just require a bolt to pass through the adapter plate and screw into the block.
BTW, the original 2 speed transmission in your car isn't a powerglide, it's a turbine 300, many times mistakenly called a powerglide. The two transmissions share little, to no common parts.