IT's damn tricky,
Bushy's have 2 serial number groups, one that are "pre-ban" having been assembled into that configuration by the factory, and a group that were sold as receivers and aren't "pre-ban" unless they were assembled prior to the ban.
I've always heard that the burden of proof is on the owner.
I guess my main question is, if you get busted for having a post-lower with pre-parts on it, what did you do to attract the ATF's attention?
Most average cops aren't well enough acquainted with the law to know the difference, and they don't carry a list of serial numbers around with them. Even so, if you've got a problem with the police taking a look at your rifles, you probably did something naughty to tick them off.
As for the ATF, if they come a knockin' you had to do something to get their attention and the pre/post issue is probably the least of your worries.
That said, I spent 750 for a pre-ban bushy with telestock-attached from a dealer.
Hopefully, that ridiculous "crime bill" is allowed to sunset next year and pre/post will be the terminology of nostalgia.