NV3500 Trany...Good?...Ratios?...

[lts70]

I have 320+hp 327 in my 70 Chevy SWB. I replaced the stock transmission with a NV3500 5 speed out of a 92 Chevy ½ ton truck (got for free out of a 600 org. mile wrecked truck). I looked every where for gear ratios and final found these on an S-10 forum. Does any one know what 5th gear ratio I would have? They had 3 different options on their site.

1 - 4.02
2 - 2.32
3 - 1.40
4 - 1.00
5 - 0.83 or .78 or .73 ?
R - 3.74

I have the stock posi-track rear-end still in the truck. Does any one know what rear-end gearing a 1970 6 lug SWB with posi from the factory would have had?

My rear tires are BFGR 285 70 R15.

I am trying to figure out if this is a good combo for my truck. If it is I want to purchase a speedo conversion box to convert the electrical signal to run my mechanical speedo. I just don’t won’t to throw $300+ dollars at something I won’t be happy with in the long run. Or is it possible to easily put a speedo gear in the trany?

So my questions are:

1) What would be my 5th gear ratio?
2) What gear ratio would my differential be?
3) Is this a good set up for my truck?
4) Is this a good trany?
5) Best way to convert to mechanical Speedo?