8.75 Rear End Question

OK...I hope you will pardon my complete ignorance. I've not ever really worked on the the rear end of any of my Mopars (insert any of several jokes here). So, I'm a complete newbie. I'll tell you what I know, what I have, and what I'm looking at purchasing. The things I worry about are the things that I don't know that I don't know.

I have a B-body 8.75 that I will use on my 68 Barracuda. Currently, it is just the housing with no pig/chunk/pumpkin in it. I have also run across a 742 chunk to put in it. Its got a Detroit Locker in it and 5.00+ gears that came from an early 70's NASCAR shop. They are in very good (like new) condition based on the seller's info and I know him from other dealings and he's trustworthy. I'm not all that interested in that gearing. But, I know I can change that out for what I want. That's all I know about it. And, I think there are more things I need to know. But, I'm not sure what to ask.

1. Will I need to find out how many splines the set up supports? Or is it a standard deal for all 742's?

2. Should I count the splines on the axles I have currently and see if it will match what this 742 has?

3. Does anyone sell an offset shackle for the A-body (I only need a 1/2 inch offset each side)?

4. Any idea if these older Detroit Lockers would be the same as today (ie would parts be a problem if something happened)? Any idea of what they might be worth?

1. All 8 3/4" Detroit Lockers are 30 spline.
2. All stock 8 3/4" rears are 30 spline.
3. I make a 1/2" offset A-body spring hanger/shackle kit.
4. Vintage Detroit Lockers are not the same as new ones.
5. New Detroit Lockers run run about $550.

Thanks for the answers.

A followup....
The guy is asking $650 for these 742's with the older Detroits in them. So I can get a new Detroit for $550. But, that doesn't include the case and the like. All I should have to do with these is change out the ring and pinion and install.So, its hard to compare. I worry about them being the older models and all. Do you think this is a valid concern? Then again, I have my doubts that I'd ever be able to kill them with what I'm planning on running.

Any thoughts on if this is a good deal or not?

I would pass.

You can buy a core 742 case for $100, so the price is about the same.

So, I figure the breakeven on this is around $300-400?