Here is a pack of  M4 x 55mm (Qty: 4) Japanese Industrial Standard (JIS) Philips Screws that are very common on the rear brake light unit of your CB750.  They are fully threaded.  

Please check these are the length on your bike and let me know if yours are different.  I stock all the way upto 85mm in M4. Please remember if they are too long you can always cut them down (tip....when cutting a threaded screw just thread a nut on first which will help tidy up the thread once you have chopped the screw).

As they are very hard to find I have had these specially made in the far east and imported them into the UK.

They are Grade A2 Stainless Steel and will not rust.  

They also match the fasteners used on nearly all classic japanese bikes. 

Please consider using some anti-seize compound, such as copper grease, on your fasteners.  

It is well worth it to help ensure they do not seize up.  

Please also make sure you use a proper philips screw driver so you do not damage the heads.  

I have both available please just ask the Seller.

They are nice quality and if you are not entirely happy with them you can return it for a full refund. 

Thanks for looking!