Guillows models are notoriously heavy. Many people feel they are not 'flying' models at all. I do believe that they fly. I built a bunch as a kid and they flew, even with crumby rubber. There are a number of people who have done successful guillows conversions. The secret is 1) a large enough model (biplanes are a good choice), 2) light enough gear. For option 2) you really need to consider lighter radios than the GWS stuff and sub-micro servos. Gear like the Cirrus MJ will work at a 10 gram flying weight for RX, ESC and 2 servos, and LiPolys are a must. The MJ ESC is rated at 5 amps and can give you a lot of motor options.

Other brands of kits build lighter to begin with and may offer better choices for conversion to R/C. Models meant for FF are always good candidates...

I really like Dave Cowell's models (DPCModels at http://www.dpcmodels.homestead.com/ for beautifully laser-cut WWI kits of normal and unusual subjects). His models are about 18" WS and the biplanes finsih out at 2 ounces or less, including radio, motor and batteries. Cost is the same or less than Guillows of comparable airplane kits.

Dave Diels (Diels Engineering at http://pageproducer.acninc.net/dielsengr/index.html) produces very nice, flyable kits of golden age and WWII (and later) subjects. His are print-wood and require cutting, but the planes are meant to fly. There is a FF cook-up of some of his kits going on over at the Yahoo FF Cookup group area (http://groups.yahoo.com/group/ffcookup/) and some very nice models are being produced.

Both the above makers provide good wood which you can use to make a reasonably rugged plane without the furniture grade wood often found in Guillows models.

Dumas Products' (http://www.dumasproducts.com/cgi-bin/dumas.storefront) kits are also good fliers, but the wood is sometimes on the light side for a model conversion made harder wood may need to be substituted in some places.

In any case, make the lightest model airframe you can manage. Put away the CA and wood glue and get some 'Super Phatic' glue. It is light, strong and goes a long way. It is like thin white glue, but it is made without all the heavy filler that normally goes into carpenter's type glues (Titebond, Elmer's, etc.). Dope, especially colored dope, adds a LOT of weight. Some of the covering films, like RA MicroLite, are lighter, stronger and more tear-resistant than doped tissue. Both of these are available from Dave Lewis at Homefly (http://www.homefly.com/). Here is a chart of typical covering material weights: http://www.homefly.com/reference/mylar.htm