The guillows kits are originally built for rubber powered flight. But the Corsair is the same scale as the pica kits and alot of the r/c combat stuff out nowadays.
I think you need to either beef up the frame if you go the gas root or better yet go to a small electric motor and leave it as is. Flight performance will be marginal so don't expect alot from your bird when it is done. I think Toni and Addie Naccarato ot the black sheep squadron had a whole bunch of Guillow kits outfitted for c/l. It was in an old model builder magazine which is now defunct.