Trans, drive shaft and differential combo questions

[Kenny]

 
Currently building a 1971 Challenger and making her a T/A as if they actually built one in 71.
Car was a factory 318, 904 auto trans and has a 2070741 case open differential with 2.73 gears.

I have a 1968 340 with 400 hp to install.
Plan is to performance build the original 904 transmission.
I have a 741 case sure grip with 3.23 gears in it.
I also have a "489" case with open differential.
SO........
Do I just swap out the 741 open for the 741 sure grip or completely redo a 498 differential?
I am wanting to go the most effective/efficient way on this already expensive build.
Was thinking that I could reuse everything by just swapping to the sure grip case.
This car will not see any track time. Just cruising.
I am not wanting to swap out or shorten the original drive shaft.
OK guys your thoughts ???

[RUNCHARGER]

Swap in the 741 with the 3.23 and sure grip. Change the the pinion seal and make sure it has the same size u-joint flange. Cheapest option and the 741 will take everything you throw at it. The 904 will work well if it is built correctly and it they pull a bit less power than a 727.

[Chryco Psycho]

 
Makes sense to me

[Kenny]

 
That's kind of what I was leaning toward.
The ring and pinion on the sure grip has no visible wear patter.
However it does not have a pinion seal in the end and thus the pinion shaft has a little wobble. Is that normal ?
Is there some kind of maintenance I need to do to it before putting it in?
Am I assuming correctly that the original driveshaft length will still be the same ?

[Chryco Psycho]

 The pinion should never wobble seal or no seal if the yolk is tight , if it wobbles something is wrong .
These use shims so if the yolk is tight & it wobbles the shims may be wrong or missing
the driveshaft will be the same length but the U joint could be 7260 or 7290 , different size , there is a conversion joint that has both sizes If yours are mismatched

[RUNCHARGER]

Hmm: What CP said. Best to make sure everything is clean, put some light grease or oil on the bearings etc. Then tighten up the pinion nut to spec and check how everything feels and how much backlash you have. If everything seems right then I would check the tooth pattern before going further. If you're uncomfortable doing this maybe check with a driveline place and see if they could check it out for you.
You don't know what you have at this point. There could have been a problem with the diff or maybe someone just took the yoke off of it and never tightened the nut down.

[Kenny]

 
Thanks !
Not versed with driveline stuff.
Think I will look for a place that can check out the sure grip assembly. Didn't thick the pinion should have any slop.
Thanks guys !!