71 chev 250 6cyl

hey yall a friend wants to put a cheap big cap HEI in the 71 chevy 250 6cyl, car if it makes a difference.. will this work? even tho they say it wont fit a 71?? just a 75-76.. https://www.summitracing.com/parts/sgt-gm34/overview/year/1971/make/chevrolet/model/el-camino . whats the difference...