The 1987-up 700-R4's (4L60's) are excellent transmissions. They require few internal upgrades and end up costing quite a bit less than a comparable 200-4R. The biggest downside to the 4L60's are the 3.06 first gear and Chevy bellhousing. They are also longer than the 200's by several inches. Running a 3.55 rear gear with a 4L60 is about the same as having 4.56's with a TH400. Talk about making a 455 hard to hold on the starting line!
The 200's have a good following, I've seen them rated to 850hp, but only by those charging BIG bucks for them. We consider them solid to at least 450hp, and OK to about 500hp. Beyond that, perfect starting line traction will quickly find the "weak" spots.
We've been building transmissions here for several decades, and typically avoid the OD's for SERIOUS high torque applications. GN's running into the 11's KILL the 200's in short order, even well prepared units. If they get two seasons out of one, that's WAY outside the "norm".
A retrofitted unit stands a better chance of survival, especially if converted to a non L/U torque converter. The torque converters are another potential failure point, and when the break they take the whole trans with them.
We ran a 4L60 in our 67 Imapla SS for many years. The only thing we broke was the converter, a "high performance" lock-up variety. It broke on the very first full throttle blast with our new engine 327cid, about 350hp. It was replaced (and the entire trans rebuilt) with a custom non L/U unit from Precision Industries, which ran perfectly for about 35,000 miles and COUNTLESS full throttle blasts, until we sold the car.
Brian, since you are considering EFI, which costs about as much as a good 455 engine, the 4L80 may be the best route? They are a pretty heavy and power robbing part, and require electronics for all upshifts, but are a very durable unit. Basically they are a TH400 up to the center support (with significant upgrades), tough as nails and you get OD as well.....Cliff
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