Need help on 8.75 rear end.

Okay this is what I have.
An "A body" 8 3/4" 741 open rear end with 2.94 gear ratio.
I know that the 742 and 489 casing will bolt in, I got that.

I know some say just buy a 742 or 489 easier said; than done. They weigh a ton so the cost of shipping is outrageous.

My question is, lol bare with me.
Can you buy, say all the stuff needed as in ring gear, seals, bearings, pinion and ect. and build the 741 casing as a 742?

Will all the deferential gears work along with the 742 new bought components. being you can just drop all the different types units in? I'm thinking yes,"chime in on this one".

I'm looking to go with a 3.91 ratio with full spool. All I am finding is 3.73's. All new product that is.

And who has the most selection of building components available for reasonable prices?

Thanks,
Michael