D60 4.55 to 4.10?

[etg]

Hey all, it's 1/2 price weekend at pick your part and I found a D60 open with 4.1 gears. I have an open D60 with 4.56 gears, turned by a new 700r4 powerd by a sbc 350 block (kinda). I was wondering what kind of recommendations you all had for lowering the gear ratio. As you've all figured out I'm wound out really fast on the freeway, and don't want to tire my newly built block out too quickly. Therefore I have a few questions, any and all answers are much appreciated.

1. Is a 4.1 downgrade good enough with a 700r4 to keep my rpms down?

2. What kind of RPMs should I expect at 70 mph running 26 inch tires at 4.10 and 4.56 (no tach, and haven't really run my truck yet)?

3. Is changing down to 4.10 as simple as pulling em out and puttin the different ones in, assuming the same shims will keep it all aligned?

I'd like to go back and buy these tomorrow, I don't think the ring and pinion will be more than 50 bucks total. I've also read that to go below 4.10 I'd have to replace the carrier, and I'm trying to stick to the low buck method for now.