Its EASIER to convert from glow to electric if you do it durring initial construction. It also turns out lighter.

You can convert a model that has ben previously flown with a glow engine installed... You'll have a bit of trouble getting the cutting tools in to do the lightening work. the batteries don't necessarilly have to be bunched in one pack... you can series wire multiple packs of the same rated cells with heavy guage wire.

The pipe tunnel location for the pack may be an excelent idea... as it should be relatively easy to direct cooling air over the batteries. (there's air inlet holes in the cowl... and an outlet hole where the pipe exited already ) Just be sure the batteries themselves don't block off the airflow...