As far as the MOT is concerned,
this is the test criteria.
A bolt in baffle should be enough to get threw the test, about £10 of ebay, if you don't have any luck borrowing a stock one.
WD40 isn't going to do anything for rust on a bike apart from make it wet, either ACF50 or if it's bad something like Krust rust will help, but generally elbow grease and cleaning is your best bet for light surface stuff.
Heel plate options are either polish them up, or paint/powdercoat them.
Cheers Mark.