best way to upgrade 690xv w/ remote start

I have done all the research and ready to begin my upgrade this weekend. This is not my first alarm install, but the most complicated and risky by far. I need some broad advice from any knowledgeable install gurus on these systems. I have a Viper 690XV alarm currently installed with an add-on remote start interface (transponder bypass) on a 99 Lexus SC400. Has been working perfectly for 4 years. Looking for more range, more channels, and a cleaner install. Only problem is that I did not install the original alarm. What is the best way to upgrade the 690XV system to the Python 990 (Viper 5900)? Should I try to keep the existing remote start module in the car since it is working, or should I dump it for the 990 integrated solution? I know there is a transponder bypass in the car, so I do not want to disturb more than I have to. I am terrified at the thought of the car entering "locked down" mode and having the car towed to a Lexus dealer to have it unlocked. Advice needed. FYI- After system upgrade. Will be adding 2 530T's for remote opening windows and sunroof (1 touch operation on each). Any input is GREATLY appreciated!

anyone? Just looking for general tips and cautions.

Pull the whole thing out and save the bypass mod. Re-install. Butter.

PS- Strip back new parts of the wire for your new connections. Another note. It's better to have one system for alarm or remote start or BOTH in a car than two different brains. Just thought i'de include that note.

"dont ground out!"

dswift wrote: Pull the whole thing out and save the bypass mod. Re-install. Butter. PS- Strip back new parts of the wire for your new connections. Another note. It's better to have one system for alarm or remote start or BOTH in a car than two different brains. Just thought i'de include that note.

This is pretty much the conclusion that I came up with. I will have "fun" locating and removing what I did not install. I will keep the bypass in the same place and remove the rest (690XV plus 555U). Not to mention solder all the connections and wrap electrical tape on all the wires. Anything else that I am forgetting?

Anyone know the if the default remote start crank time will work on the Lexus V8? Just any FYI's are appreciated.