Yes, the magnets will work fine. That was a really good suggestion from fellow members. If I have any issues with rotation, I have another trick up my sleeve, which makes great sense - take advantage of the screw holes themselves - connect short shafts to attach to the case top and pop into the straw (screw) holes to keep position, the magnets to hold the plate in place.
Anyway, I have two hours for project work today, so let's crack on with it!!
Kyo - Thanks for the comment. By the time I finish with this portable it will look near commercial quality grade and something I will be very proud of. I hope others share my vision and buy some of my case kits too, that would be lovely!
UPDATE:
Seems the Poly-weld plastic glue doesn't like to stick the PSone plastic to the Plasticard I used for the vacuum forming. Not sure which surface is the issue yet; so I had to use hot glue. Sticks both surfaces really well (I don't have good epoxy glue, tried some before and it was awful, so staying with that I know about!). Not a problem anyway; hey, I live in the UK, so the weather on a hot day (yes we get some occasionally) in a car left out in the sunshine, only gets to 36c, at worst case
Also, cut out the last of the shoulder buttons.
I had wanted to have the memory card to slot into the system at the top of the case; would be ok, but will be close to the CD mechanism. If I move the batteries a little, as in the pic below, there is plenty of space for a memory card slot at the bottom of the case (and have the memory card sticking out about 9mm so it can be easily removed and replaced as needed).

As you see, there is plenty of room for the PSone controller boards too.
Out of time today, tomorrow I will get the memory card hole cut out and also an on/off switch; and build a surround for the inside of the CD tray and also a plug hole for recharging the batteries.
Case will then be complete and ready to spray paint.
Assembling and documenting the internals for the system and finishing the project is within sight now; will be done before Xmas; although I doubt I will have time to get everything documented and prepared to sell my kits before Xmas as there is a lot of work to do to get to that stage; first half of January however is very achievable.
The batteries will be secured in place and connected in parallel to give 7.4v at 4000mA, which should last about 2 hours 10 mins playtime. I will connect a plug to the system so I can recharge them, by connecting them to a proper Canon BP-911 charger (does BP-915 and BP-911 cells), so safe to recharge them fine.












