Have been looking at technical data of these engines and could not find any differences between them. They all have 82,7 mm diameter cylinders, they all travel 93 mm, all have 1998 cc. But main question is: are bottom ends interchangeable between different types of heads 8v from F3R and F4R/F7R 16v? For example I have F3R and fit it with F7R head. Will this work?