under new mot regs I think you will find its a fail if insecure, wich yours is you say. dont have to be sheer bolts ,if you can get old ones out fit normal bolts so its secure.
easy if you can weld !! you need to get all the plastic trim off first for proper look . be prepared for bit of a shock as that trim hides a multitude of sins.
see if I read this right..piston ,seals & bearings fu@ked . you fitted them....so you rebuilt engine ?? now blowing oil cos to much back presure .yes/no ??