Can the heads on a 1999 RS be removed with the engine still in the car? Is SOHC version.

not easily, but yes.

 

it helps if you undo the engine mounting bolts on the bottom and at the dogbone on the fire wall, and lift the engine several inches.

as-is - it's nearly impossible to do or to do properly.

 

but remove 3 fasteners - the lower two 14mm engine mount nuts and the bolt for the top pitch rod.

once that's done jack the engine up a few inches and it's rather easy.