Or alternatively, 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 {TAIL ~ other suitable parts} 
Or alternatively , 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 { TAIL ~ other suitable parts }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL