You should be able to use small mechanical retracts made for EP's.

Note however that doing all this will be completely up to you. You'll need to "engineer" things to get a proper fit and operation.

As for the WHEEL WELLS forget about the plastic inserts as you'll have a hard time finding them.

You could try your hand at forming a plastic bottle, using a hot air gun... but IMHO the easiest thing to do is to cut out the wells to size, and "warp" balsa into a circular shape to fit the circular opening.

Thin balsa bends easily when wet, so you could soak balsa sheets to obtain the circular shape of the wheel well walls, let the sheet dry, and glue the walls into place.

Once done, cut off the excess, sand and paint.