Radio, servo requirements? Failsafes?

Gassers don't get on well with the old 27mhz AM radios. The 27mhz band is very close to the frequency of electrical noise naturally generated by gas engines when running. Avoid 27mhz.

40mhz FM is considered minimum requirement, but in this age of DSM and FHSS (2.4ghz crystal free systems), there's no excuse really to spend $1000 on a car and skimp on a cheap radio.

Go for a Spektrum, Nomadio, Futaba FASST or Airtonics FHSS system, if you have the cash, it's well worth it especially with a big fast car, to know that you are not going to be interfering with anyone, or have any glitching issues. 3ch radios are normally required either sooner or later for gas cars, though that does not apply for an HPI Baja 5b which will not be raced (there's no slot for a third servo on the car, and since not racing, no transponder is needed), but most large scales come with a third or even a 4th servo slot, for dual servo steering, or for additional disc brake systems, so 3ch has become the norm.

Servos (especially for steering) are obviously much larger and stronger than their standard size counterparts. Most servos available in the 1/4 size servo market are adequate for the job of steering a stock gasser, and the differences are whether you want to get a faster servo, or a digital servo, or a heavy duty metal geared servo, etc. There is one steering servo that does it all for a reasonable price, it's a large scale digital servo, with 16kg@6v holding power and 0.10sec/40deg/6v transit speed. It's called the Multiplex Rhino Digi4. Great servo.

For the throttle, some models provide only a small servo slot for a standard size servo. Some others give you the option to use large scale servos for throttle/brake duties as well as steering, but for most purposes, one strong (200oz-in or more) standard servo is adequate to pull the brakes and operate the carburettor on one of these cars.

I guess it goes without saying that servos for these cars are an important item, due to the size and weight of the car, so don't skimp here. Good servos will last you, bad ones will fail on you, and failures in control can be very expensive

Most RTRs come with rubbish electronics, which should be upgraded immediately.

Failsafes are essential for gassers, more than any other scale. If you have a 30lb truck run away from you at 40mph, you are not gonna be able to catch it, and chances are it will either do serious property damage, or worse, put someone in hospital with multiple leg/foot fractures. I can't stress enough the importance of at least a basic failsafe, and ideally one that can cut the engine as well.