Wait a minute guys ...
The GS450 wasn't a shaft drive was it ???
https://www.motorcyclespecs.co.za/model/suzu/suzuki_gs450a%2081.htmDang ! it was !! In only one version
That weld on hard tail is made for the chain-drive version ... and ... you'll have to change the lines of the bike to match the angle on the hard tail or you'll end-up with a "funky looking mess" .
Whats wrong with leaving it in a 450 frame ?

You do realize your contemplating digging a money pit ?