I believe all 7th generation Suburban's (1973 - 1981) used a common floor pattern so the seat bolt holes should all be there in the floor.
They all use a common wheelbase of 129.5 inches...
Question...Are you changing the door trims?
Are both vehicles fitted with either wind up windows or power windows?
Not sure about 3 point seat belt mounting points on door pillars....I dont believe the 74 has them ....
Hope this helps out...
