It appears that your running gear needs complete replacing as it not worth it to spend money on this setup any more .
all depends on your budget , the easiest is to install a 7K with G-52 if thats fits in your budget otherwise you have to locate a good 4K/5K engine and install a replacement K-40/K50 transmission. I have a very good K-40 lying at my place in islamabad if you want that .
Though 5K is very heavy on fuel being non efi .
If you in Pindi /islamabad than you can contact mechanic Sohail near Harley street or Haji Mukhtar in sadder ,
inbox me if you need any further information .