Are the tube frame suspension kits from HT Motorsports any good? Do they actually make a difference from stock suspension?

Yes, and No...
Depending on your driving style, they may be of no use to you.
The biggest advantage to their front systems, over stock, is the adjustable coil-over shock at the front. This allows for more options in spring rate and damping.

The rear bump steer correction system does what it was designed to do, but rebuilding the rear suspension will accomplish much of that as well.

-Dave

adding: I have their systems on my 85.

[This message has been edited by IFLYR22 (edited 11-20-2011).]

That's a pretty broad question. Although tubular steel control arms are generally stiffer that stamped steel ones, I doubt anyone here has actually done a controlled experiment measuring the bending and torsional stiffness of stock and HT arms and compared the results. Certainly replacing your OEM arms with tubular steel arms of the same geometry isn't going to make a difference you'd likely notice from a seat-of-your-pants driving experience. On the other hand, the bushings that hold the arms in place are going to make a much larger performance difference than what the arms are made of (unless your using spherical rod ends for pivot points). Some might argue they felt a big difference after replacing their control arms, but that's more likely because they replaced the bushings at the same time.

Aftermarket arms are more suitable for people who want to:

1. increase the track width by using custom length arms;
2. improve characteristics like the bump-steer issue on the rear of '84-'87's;
3. install coil-over shocks be to able to adjust ride height;
4. replace damaged stock arms; and/or
5. improve appearance

Thanks, that is all very helpful information. Are they much lighter than stock control arms?

Although I have both a set of OEM and HT control arms sitting right here in front of me, I can answer your question because the HT arms I have are 3" longer than stock so they would throw the weight comparison off. Sorry.