A quick semi how-to for thrusters:
I purchased some thrusters from eBay (make sure you measure how big yours are according to the largest diameter at the bottom in millimeters (mm)). Kind of expensive I guess at $10.50 for 4, but that's the nature of gunpla itself haha.
Figure out where you want to put the thruster. Usually there is already a place for you to put the hole in, or you'll have to cut off a nub for the plastic thruster to go on the plastic kits in order to drill.
Make the hole pretty deep. Note: If you have a shallow piece, you can also snip the long pole to be shorter.
Test fit the part that will go in the hole once you're done.