So I gather you already got the tools you wrote of in the other post.
Why aren't you worried about the machining? Do you have someone lined up to do it for you? Has he ever made a gun part?
By the end of WWII Ordnance had determined the steel and hardness requirements of 1911s were fairly stringent. Yes, you can machine a part out of old train rails, but don't be too surprised if it doesn't hold up in use.
Which aluminum are you planning on having your friend cast? In the long run it might be more effective to research what blend and hardness you are looking for and simply buy a frame block already formed and treated to the desired hardness. Aluminum can be tricky to machine, chilled aluminum even more so.