You could try and pick a real people who have the body size and shape closest to the characters in your story and check their stats. Usually any bio or profile will have stats once you search for their name.

Beside WPW, you could also try GetBig dot com.  Some of the entries include the figures for the competitors height and weight.

Link: http://www.getbig.com/almanac/almanac.htm

You can also use range tables for height and weight comparisons, albeit most are for non-FBBrs, but you can still attract base info and project from them.  They can be found on-line, run a search with Google.

Good luck!