Questions about S/36 files

A couple of questions about S/36 files, prompted by a potential new customer whose whole native system is apparently set up around them:

First, while I've occasionally futzed around with totally flat, non-keyed files, and while I've used program-described mode to circumvent level-check problems on externally-described files that change regularly, but in a manner that's under our control, I don't have a lot of experience with actual S-36 files. Am I correct in my understanding that an S-36 file can be both flat and keyed at the same time? Is there a convenient way to create a file indistinguishable from an S-36 file on a V4 or V6 box that doesn't have any S-36 emulation installed?

Second, can SQL access an S-36 file? Is it difficult?

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JHHL