I understand that you have the receiver's and action available and would like to use them and that's all good as far as it goes . The #4 made into a Lee Speed style rifle is a bit like a ruger #1 and a Farquharson , they're both falling block's but they're a world apart . Now having said that a #4 can make a damn fine rifle , wood is available from Gunparts corp which could be restyled to look a bit more Lee Speed like . Reboring the barrel is doable although I'd say an A&B would be more economical but then, it lack's the nock's form , the magazine could be modified / shortened , or you could find one made by Gibbs who converted these to 45/70 years ago. The normal Lee Speed rear sight is pretty much unobtainium unless your luck is so good you win lotto regularly ,other than that if I get time I'll compare the butt plates on my Lee Speeds and the military one.

http://castboolits.gunloads.com/showthread.php?t=14784

Here's a Parker Hale effort from the late 60's

Cheers
Pete