Thankyou- id have had to look through diagrams for something id have never "needed" to know, but been kept awake by. You're a godsendThat threaded boss on the cylinder head is a motor mount boss. Since the front and rear heads are the same part, they both have machined motor mount bosses. However, they are only used on the front head. They are unused on the rear head, except to secure one of the vacuum dampers on the TLR (right side).