Depends on what "modern" suspension you're planning to convert to. The stock Anglia frame is a simple, lightweight frame, and will need some reinforcing to even swap a later engine, and straight axle to. But I've known guys who bent up round tubing to add cross bracing to the stock frames, and make them stronger.
If your plan is to swap in independent front suspension with control arms, then it will take a fair amount of work, and a front frame swap might be a better choice, IF you can find one narrow enough to fit under these diminutive cars. A fair number have been fitted with Jaguar sedan front suspension, which can be easily narrowed, and will give you a nice ride, modern components, and Chevy bolt pattern. Most people use the older 70's and 80's Jaguar sedans as donors.