Happy to see another 450 rise from the ashes!
Careful with that car battery jumping stuff, you can 'melt' things.
Charging the battery is much safer. If you have a hill or can do so, push starting might be worth a try.
I would recommend checking your stator and regulator/rectifier w/a multimeter. These systems maintain/charge the battery when riding and a new battery should not die out easily.
Check for spark too. Fresh plugs are a way cheap investment. Is that CDI 30 years old? A new CDI is not a cheap investment, but well worth the peace of mind (for me at least)
A full tune up is always a good idea!
With a service manual and this site, you'll be rolling soon!
'86 CMX450 Gin-ba
'87 CMX450 Kuro
'86 CMX450 Tabo
'90 CB-1 Seishin
'86 CMX450 Uki