The plastic receiver case on the 89 may be something custom formed out of car body lexan, similar to AE gear covers. The seam looks somewhat crude, and the fit is pretty specific to the circuit card. I do not believe this is a modified container of any kind. There may be a way to make one.
1) Cut a block of wood in shape needed,
2) Pre-Heat sheet of lexan in oven,
3) Place heated sheet of lexan over wood block,
4) Pull vacuum.
Two wood blocks would be needed to form the two halves of the box. Then you would glue the halves together.
Here is a quick Youtube video showing the process for an RC Truck Body:
https://www.youtube.com/watch?v=ooVBJbYac_4[url][/url]
[youtube]ooVBJbYac_4[/youtube]
It would be cool if one of the replica RC body companies would be willing to take it on. (OldRC, Team Blue Groove, Mr Lexan, ???)
Mark