Well, the cold struck my RS about a week ago and my engine went to $h!t, it seemed to be my TBI injectors. I've wanted a 670 for a while and compared it to the price of new injectors and tbi rebuild kit....favor was to the Holley.
The unit itself has pretty crappy molding, but otherwise looks pretty good. It was a simple bolt on, you just have to splice the injector wires on the wiring harness. Also, the mount(??) for the throttle linkage is on the reverse side, and there is only a hole with no mount for cruise control. The adapter/gasket to fit the stock 1 11/16" bores on the manifold is probably a 1/4"
Any ways I should start by saying I ordered the 502-5(for 305s, 57lbs injectors), and my engine was running like crap before installation-a lifter is hitting pretty bad.
The performance of the engine now, is better than when I first ran into the problems a week ago, Though it is still not even close to where it was before the cold hit. I'm basically saying this because I can't truelly judge what the new TBI did for me.
It did take a few days for the computer to adjust, and I did get one SES light. I can tell a difference past 3000 rpm as she pulls stronger and to higher rpm, though anyhing below 3000 seems to have suffered, though like I said before, I think it's my bad lifter causing much of it.
Anyways, it seems as though once I get the lifter fixed(installing a LT1 cam as well), the 670 will have been worth it, and isn't to much for the 305 as many people insist. Any questions on the TBI unit, and I may be able to answer a few.

**I know people will probably rag on me for buying the 502-5 and not the 502-6, but the vendor was outta stock for the 502-6 and I needed a TBI right away.

 

I'll attach the picture again. The cruise bracket can be welded to the holley bracket at the "bend" of the stock bracket. It has to go back about 1".

 

I just put my Holley 670 in and had the same linkage problems. I had to weld up a new throttle bracket and find an extention for the cruise control. I had it a little easier, no tranny cable with a TH400. May have been easier if Holley had centered the body on the adapter.