Well, not actually problems, but more like challenges.  Most of the Classics plans do not show mufflers, uniflow tanks, sliding lead outs or weight boxes. Now start adding these and all kinds of problems or challenges pop up. 

Ty, you are correct in that the old designs present many challenges especially when it comes to incorporating some modern concepts.

Although my Barracuda isn't a Sheeks design I had to work out several problems during construction. For example, the sleek narrow nose had to be widened by 1/16" or I wouldn't have had enough room hollow the cowl to clear the cylinder fins and exhaust flange of my Rojett .40. The nose also had to be lengthened by 1/2" because of my engine choice. Otherwise, there wouldn't have been enough room between the engine and nose gear former to install a 4 1/2 oz tank. I'll have to custom build the tank as well.

The original Cuda had very thin wing tips (3/32" core sheeted top & bottom with 1/16" balsa) and did not have a leadout slider. It was a challenge to add that feature. I think mine worked out very neatly, at least I'm pleased with it.