I have done two six cylinder Gremlins with Clifford aluminum 4 barrel intake and twin headers. They run better than the stock V-8s acceleration wise and still get great mileage if you don't change the cam or differential ratio.

On my '77 Gremlin I switched the sloppy unreliable motorcraft distributor to a GM HEI and the performance difference was very noticeable. This engine already has the aluminum Clifford 4 barrel intake and 600 vacuum secondaries Holley and twin headers. My previous did used mechanically driven secondaries, but was a 4 speed manual transmission.

Here is a picture of my engine with details about how I did everything:
http://www.upmpg.com/projects/amc_gr...etrain_025.htm

This engine runs really good and has better than expected power and accelleration. I used the vacuum secondary Holley this time around because of the automatic transmission. However, I am building a 258 for this car that will have a mild cam and performance cylinder head. I will replace this Holley for a mechanical secondary carb at that time (probably).

It isn't hard to do a distributor change on these engines. Here is an article on the how's and whys:
http://www.4x4wire.com/jeep/tech/electrical/hei02/

The GM HEI distributor is a one wire distributor and easy to wire in. I really found it easy to install. Just read this article first before doing it.

Doing a AMC six this way is damn fun! They sound incredible and run great. I have to open the hood a lot to prove it's a six.