Hi jeflon and welcome,
Oh my, didja get a pile of parts along with what's shown in the photo or is that all of it?
You can look through the list's classifieds and hopefully find all you'll need to get the bike running.
for a start, you'll need to install the front engine mount before you even turn the motor over.
[edit]
your post #3 leapfrogged this one.
Before you ride the bike anywhere, check out the front forks & wheel.
All single front disk XS650s have the disk on the right hand side and yours is on the left.
The '75 XS650 had it's brake caliper lugs (there are lugs on both sides because other market XS650s ran dual disks) on the front of the fork sliders and yours are on the rear.
Either the dreaded PO has reassembled it wrong &/or the forks are from a later bike.
Note that lotsa XS650 parts swap between models & years like LEGO so anything is possible.
[2nd edit] your wrongside-mounted front brake disk is the 2-part disk that goes with the 34mm fork tube brake caliper.
But as the front brake caliper ain't there; check the fork tube diameter to see what's up.
If it's a 35mm fork from a later year the wheel itself will still fit but it'll need the later one-piece brake disk and the later model caliper or things won't line up.
