Just bought a '95 Tacoma

So I just bought a '95 Taco. It's a little rough around the edges but I've been fixing it up. My main problem I ran into is the front diff is rusted out internally. I have managed to savage everything but the ring and pinion. After looking up my at my rear axle code 'B03A' an 8" ring 4.100 gears and 2 pinion open axle. My front axle is a 7.5" ring 4.100 high pinion reverse cut gear. I haven't gone through the dealer Yet to see if they offer the 4.100 for the gear, but no one seems to offer this gear size in reverse cut. This leaves me in a pretty pickle to say the least. My options seem to be limited, replace the both gear sets and go to the next higher size at 4.56 or hope someone knows a site where I can pick this up. Now with all that being said I have found a factory posi rear diff on craigslist from a '02 Tacoma. I figured if I'm going to replace both sets of gears might as well replace the carrier on the rear with a posi. But I'm not sure if that will just be a straight drop-in replacement. Also not sure if I will have to get a specific gear set for the rear since it's would be a Posi. It seems like they had different gears for the rear depending on if it had a locker or not. At least that was it seems like from some of the sites. I'm also assuming while I'm at this I will have to buy a while new bearing and shim kit if I replace the ring and pinion for the rear. Looking for any help to work this problem out. If you have anything that can help me out please let me know.

Additional Info:
Current Tire Size: 30x9.5R15
Future Tire Size: 33s on either R15 or R16
Axle Code: B03A
Transmission: Manual
Transmission Code: W59
Engine: 2.7L
Drive Type: 4x4

Also does anyone have any info on how to change my speedo gear once I goto a larger Tire size?