I don't see how Hinson's mounts could be bad, unless they straight up don't fit. I've spent my share of time on the hybrid section her and on LS1Tech and haven't heard anything about them not fitting properly. There are, however, more companies out there other than Hinson if you want to buy some mounts. As far as making your own, if you have a welder I'd get to it if I where you. Don't pay for something that you can make with a little effort.
I don't believe that any LS1 swap kits use the stock trans crossmember to mount the LSx's transmission. Although you could mod the stock crossmember to accept the new transmission with a welder and a little time.
Aftermarket K-Members aren't needed for the swap. All you need is a GTO oil pan (front sump) and you're good to go.
Unfortunately I don't have a 240SX so I can't help you with that. LS1 Z32 is how I roll.