Or alternatively, {TAIL ~ the assisting beams} 321 and 323 can be replaced by other suitable parts, and {HEAD ~ the assisting beams} 322 and 324 can be replaced with other suitable parts 
Or alternatively , { TAIL ~ the assisting beams } 321 and 323 can be replaced by other suitable parts , and { HEAD ~ the assisting beams } 322 and 324 can be replaced with other suitable parts
OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH