Actually the front end IS your immediate problem because until you get your motor set the driveshaft has no bearing on anything. Also the shaft can be cut and welded (by a qualified shop) to fit your set up.
That front suspension is NOT a second gen F-body and is NOT a G-body. It also is NOT a truck but it is a true mess which needs to be completely redone in order for YOU to KNOW what you are running and for it to be installed safely. THAT does not appear to be a good and safe installation.
Either get a suspension system from a known vehicle or better yet get a new frame and install an IFS kit.