The answer is: it depends. What do you want from the airplane? I have a Cox Centurion of the same size and mentions by 1967brutus and can confirm it flies nicely as a two channel airplane. Fuel proof dope is still available through Brodak. If you don't want to mess with dope and tissue, iron on covering is still a thing. When dealing with things like the Guillows kits it is important to remember that most of them were designed in the 1960's and 70's. Radios have come a long way. Receivers are much smaller. You can use good quality micro servos on an .049 plane and mini servos up to a .15. Guillows planes also have a construction style that as noted above can be kind of fragile and you will have to do some re-engineering for control surfaces etc. So, yes an .049 can be made to fly the airplane just fine. If you want throttle and any amount of scale detail then step up to an .07-.10 engine. A throttled Norvel .049 could also be nice.