Mixing different converter parts has been performed for decades. The shop should be able to build converter you need for application on the T-400 trans.
The following does not apply to the T-400 in the OP discussion, just an FYI on the power glide shaft tube comment:
Power glide pump stator tube does not need bored out for 30 spline turbo sized shaft. Often the end of the stator support tube is machined out for a bushing to support the end of the turbo splined shaft.
That bushing is needed when the turbine hub inside the converter does not have a bushing on it. With the bushing in place you need to have a shaft with proper holes in it for fluid flow into the converter. You need a busing support on the turbine hub or the input shaft end at the stator tube.
There are larger shafts for the power glide, that can require a full replacement of the stator tube and pump. Must be careful here for proper matching parts
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