Modifying any kind of radio to work on FRS is illegal. Don't do it.
If you and your buddy want to become hams, check out www.arrl.org
for info. Cost is very low but requires a considerable investment in studying for the test. Kids as young as 6 have passed, it just takes determination. VHF range directly from radio to radio (we call this simplex operation) will be about the same as a properly installed CB (basically 2-10 miles depending on terrain) however, there is much less interference than on CB. We also have "repeaters" that will relay signals from mobile stations so that everyone within a 50 mile radius from the repeater can hear each other. HF range varies considerably from a few miles to world-wide depending on the frequency. Finding a clear channel on HF is very difficult, if not impossible. Note that no one "owns" any frequency; we all have to share.
I assume that you want something with more range than FRS. Check out the Multi-Use Radio Service. This new service allow the use of 2 Watt Business Band radios on about 5 or 6 of the so-called "color dot" channels that were formerly reserved for business use only. No license required. You can buy the radios from Radio Shack.
The General Mobile Radio Service (GMRS) is another possibility. If you and your friend want to help the community you can join REACT (an organization of people who help stranded motorists, etc. using CB and GMRS). There is a fee (I think $80 for 5 or 10 years) for the license. PRYME makes radios that work legally on both GMRS and FRS.
Of course, I'd like to see you take the ham radio route. We need new blood, and hams with 4 WD vehicles are especially useful in emergency work. However, we only want you if you will abide by the FCC regulations. That means get your license, use properly constructed, legal gear, operate in accordance with accepted practice and be courteous to others. We don't need more CB types operating illegally on the ham bands.