It was an after thought, like most small U.S. made cars
The Pacer was hardly an "afterthought." It was intended to be revolutionary. I had never seen one till I was an exchange student to near Chicago in 1981. They certainly caught my eye, and I did a bit of reading up on them.
The thinking behind the development of the Pacer was that people were looking to smaller cars, but still wanted more space inside. AMC figured that making a car shorter but keeping it wide and tall was a way to give people what they wanted. But AMC were a much smaller organization that the big 3 and like several previous models, AMC continued some old-model AMC technology to keep costs down. AMC also used some components common with rival cars, IIRC the Hornet (and thus probably the Gremlin?) used shock absorbers from the Ford Falcon, for example.
The Pacer's engine was intended to be a brand new rotary engine that AMC was going to source from GM. This would have been compact and light weight. But GM canned the rotary engine project at the last minute, due to a combination of spiraling fuel costs (rotaries were notoriously thirsty) and severe reliability problems with rotary engines used in German NSU Ro80 cars, which eventually led to such high warranty claims that NSU folded and was swallowed by VW group.
So AMC had to find an engine for the Pacer at the last minute - and decided to shoe-horn in the ancient AMC six, which really did the Pacer no favours. It was much longer and heavier, which ruined space efficiency, gave heavy steering, upset handling and drank fuel.
I really liked the styling on the wagon version of the Pacer - it was a better balanced look. The Pacer was at least cleanly styled and not over-decorated like most American cars of the time. I'm also a fan of the styling of the original AMC Hornet, though later updates with the huge bumpers ruined the clean simple style of the Hornet.
BTW, Hornets and Matadors were assembled here in Melbourne by Australian Motor Industries from imported components. They were expensive and sold in small numbers. They were NOT badged as AMC, but were sold as Rambler Hornet and Rambler Matador. AMI also assembled Triumph cars from the UK and some unheard-of new brand from Japan called Toyota... Australia was Toyota's first export market, starting in the late 1950s. Rambler assembly stopped in about 1975, Triumph continued till 1978, then AMI only assembled Toyotas. AMI was eventually taken over by Toyota and it became Toyota Australia.
One AMC Pacer was brought to Australia by AMI to display at the Melbourne Motor Show, but it wouldn't have worked well as right hand drive. The passenger side door was longer than drivers side, to encourage rear seat passengers to get out on the passenger side for safety, but that was wrong way round for Australia and AMC wasn't going to change the panel pressings for a small RHD export market, so the Pacer was never sold here.
