I fitted metal Sparco ones.
Not sure what tips to give you except take your time.
It's a pain working with a drill and other tools in the drivers foot well.
On mine, the throttle pedal is plastic, so (if yours is the same) be very careful when making the holes and doing up the nuts.
Not sure if I've got big feet

, but...
One thing I've never liked about the Scoob is the lack of room to allow your left foot past the clutch pedal to reach the footrest.
By adding a pedal extension, be careful not to further limit this room if you can.
Be sure about the exact position of your new pedals before drilling the holes.
Use chalk or better still a fibre tipped white/silver pen to mark out where the holes will go. Feel around the back of the existing pedals to ensure that the nuts will not foul the pedal arms.
Lastly, take the time to get 'em straight or you'll regret it later...
Have fun
Rich