missing chunk of frame looks like PO was doing a uni-filter/carb clearance mod and never finished. Look up user "JerseyDevil" and check some of his threads in his "statistics" in his profile. he's done the mod on a couple of his swingarms.
The carter manuals are pretty good, service manual has a full engine rebuild step-by-step here's the link to the pdfs.
http://www.carterbrothersparts.com/c...others_manuals
I may have a spare side plastic for around the fan, with these 150s, you do need to have all the plastic shrouds on them for cooling air flow.