They should swap easily... Might be some minor appearance difference (headrests posts?), and the upholstery pattern will be different, but not too far off (both use vertical pleats)...
http://www.chevellestuff.net/1969/interiors/int_bench.htmhttp://www.chevellestuff.net/1969/interiors/int_bench.htm
http://www.chevellestuff.net/1970/interiors/int_bench.htm
http://www.chevellestuff.net/1969/interiors/int_bench.htmhttp://www.chevellestuff.net/1969/interiors/int_bench.htm
http://www.chevellestuff.net/1970/interiors/int_bench.htm