Upgrading rear end gear

[dragginass]

Well considering I have the factory 3-speed in my 71. And I have never used 1st cuz it is such a low gear. And that 3rd tops out at around 65. I was considering going to a much higher gear ratio in the rear end so that it would bring first into a range of use and would up my mph in 3rd for interstate travel.

So my question is....

1-Is this feasible to do? (Such as will it be worth the time and money?)
2-What is a good ratio to run with for my rear end as in how high can I go before it is a serious strain on the motor?
3-Will I need to change my chunk if I go with a ratio much higher than factory?