Today I picked up my freshly covered seats from my seat guy. Here's a before and after. We didn't touch the tins or tracks, just new ACI cushions and Legendary covers. The original springs were repaired where needed and the drivers backrest frame was welded due to poor or missings welds from the factory. FB_IMG_1527961800854 by Grandpas67 posted Jun 2, 2018 at 8:25 PM IMG_20180602_004639 by Grandpas67 posted Jun 2, 2018 at 8:25 PM
I'll have to compare the 51 year old backseat to the new covers and get back to you. Just based on what i saw of the old seats and the new covers it was pretty spot on.
Got a deal from Rick at wellington classics for $225 on the cushions. Covers were $360 and ACC carpet kit $160. We used the gm a-body mixed set due to the attach point down the middle of the backrest. http://www.americancushionind.net/product/67-70-mixed-a-body/