It depends on what you mean by "easy", and what you mean by "modern". Depending on your true ability, and your budget, anything at all can be either easy, or hard. As for "modern" a 302 or 351 Windsor is no longer considered modern. They are Ford versions of the belly button motor (yawn). Neither will truly just "bolt in". If you can deal with and improve certain issues, the y-block is fine. That will bolt in. If you want something bigger, and with great interchangeability, an FE will actually bolt in. All you have to do is move the radiator forward by reversing the mounting bracket, and installing the exhaust pipes from the mufflers forward to the engine with pipes from a 58-59 FE engined car. Thus endeth my opinion. And you know what they say about opinions.