the plans show how to mount the landing gear more forward in the wing for the tail dragger setup. It's no more difficult than the trike version. I think you may have all of the necessary materials in the kit to build it either as a tail dragger or a trike.

I've been running a K&B .65 (taildragger setup) on mine for years. Gets off grass with no problems. I don't know much about 4 strokes but I think I would look for something a little larger than a .70