I would go with the HF you have since the aero is good for the highway, unlike the 79. A CRX of that gen can also be a very comfortable cruiser since they come with comfortable seats, and decent interiors (unlike the older ones in my opinion).
On the never-ending quest for better gas mileage...
Thanks for all your help everyone, I think I'll go with the CRX. I've started repairing the rust and it's going well so I think I'll drive it as is to see what the mileage is like then swap the motor later on. I'm interested to see the improvement with the new motor in the same exact car with the same transmission.
what sort of mileage does the '79 civic get as it is? I would think it would be decent, seeing as how it has a 1.2L engine, if it has a automatic, or the 4 speed, then I would swap in a 5 speed, and I suspect that the 5 speed FE tranny from an '80-83 might be to differnt to drop right in, altho it would be worth checking on, there is one in Portland OR with 93,000 miles on it for $150 from a 1979 civic.
If you are looking for more power, I've seen photos of older civics that people have put muliti thortle body fuel injection setups from motorcycles on, as it sounds like you have some expearince with fabricating, and making things work.
I've only driven the Civic about 500 miles and it got 36 MPG mostly highway between 55-70 MPH. It has a 4 speed but I believe a 5 speed from a CVCC of the same vintage would bolt in. I think I just got lazy being that the CRX is the easy way to great FE.
If you pick the CRX HF it would be great if you could document the whole transplant as there are more HF drivers here that will consider putting a VX engine in at the point their engine gives out I think (like myself even though that can be a while since it only has 148K on it now).