lunch money

So I have a metals class at school and I have a idea for a project. I have never attemped to fabricate any thing bicycle frame related. So I'm looking for input, opions, and general guidance as to wether this is a realalistic idea.
What I'm working with is a 56cm Colnago sprint or something and thr top tube cracked half way round the front internal cable routing, otherwise in great shape.
The other frame is a 60-61cm Gios professional with a rusted through top tube, otherwise its not bad.

So the 56cm colnago is my size and I would like to use this as the frame in which will be used in the end. I am prepared to unbraze the Gios and use this for donor tubes/lugs...

I dont want to just throw a top tube in, but since this is a art class I wanted to do something similar to a flying gate. I a big fan of the 70's english tt bikes with crazy short wheelbase...Bottom line is I would like to have a unique yet classic and functional design when done. Please help, I can take pictures and include tubing lengths and dimensions.

To start I will replace the top tube on the colnago, unless the crack is repairable (doubtful). Then plan on cutting the seattube from bottom of seatpost and unbrazing from the bb. Adding a donor tube from the Gios as new full length seat tube. Then adding the two new seat stays, possably from the gios seatstay. I'm most concernened about the angle of the new seat tube coming from the BBshell. The angle is going to change quite abit, will the shell conform to this change if so how? Also I'm assuming I will need to take the rear in a bit by shortening the chainstays. Not planning on taking apart anything on the colnago that doesnt need be...So am I out of my mind or is this doable for a first timer...Thank you for your help!