now that you have the front suspension in, the rake angle change is going to affect the front end geometry. you would want the lower control arms to be level, side to side and fore to aft, at ride height. hopefully that is where it is now. you could get around this, partially, with different drop spindles to effect the drop of the front end and keep the control arms level side to side. the problem comes when you change the rake angle of the frame the suspension is hung from. you automatically change the fore to aft angle of the lower control arm pivot shaft when you do this. like said, you may change the anti dive as well. some research required.
if you decide to go ahead I suggest to mock it up and see what the angles will be and if you can live with it. worst case scenario you could cut and remount the cross member to be correct. tons of work. you could also sell the frame you fabbed and start over.
for the notch you could simply lop the section of frame off behind the cross member ahead of the wheels somewhere, then fab a c notch section from rectangular tubing and weld it in. it may look and operate better than the alternative. you could then mount the shocks nice and neat with less weight from gussets and plates etc. see the link for an idea Scott's uses. really, if you wanna keep the stock box floor, you don't really gain much except possibly some dental work if the suspension bottoms out, which is likely. maybe private message ogre, he has the stock frame with a small c notch and is driving for a few miles now. he would have a good idea as to the number of times you may need new dental work. he is using leaf springs but has minimal suspension travel back there.
the other link is for brackets and such for a pretty good price. Canadian dollars so the USD goes pretty far. I know your buddy is cheap as well though, maybe get some ideas while looking. the last is just a quick google search on terminology for ifs and how things relate
http://www.scottshotrods.com/1955-59...truck-chassis/
https://welderseries.com/?_vsrefdom=...SAAEgKb9fD_BwE
https://www.hotrod.com/articles/inde...nt-suspension/