by replacing the 307 in the f/wood brougham with a 425 olds and thm400 behind I am assuming a larger radiator will be the order of the day.
does a 472 or 500 radiator fit straight in or ?? are the mods substantial ??
cheers mike

A 425 Olds is an excellent choice. That baby's gonna have some power. All GM rear drive cars have standard size radiators. All you really need to do is measure the width and height. Any older Caddy radiator should bolt right in. I think any heavy duty chevy truck radiator will work too. You could just run a temporary temp gauge (if it doesn't already have one) and see if the stock radiator can keep up; it might. Enjoy the ride.

I replaced the radiator in my '90 307 and it originally had the 1-inch wide radiator. But I but in a 2-inch and it just seemed to run a whole lot better.

Did you know that radiator shops are a good place to take a leak?

You shouldn't have any problems finding a radiator for it, diesel cars had bigger rads and built in oil coolers. 425 Cad cars would be the next best choice. A friend of mine's dad dropped a 455 Olds in place of a 350 Diesel in a 79 98 Regency and didn't fret cooling problems. Another good choice would be a 400 Pontiac Catalina/Bonneville from 77-79.

I would ensure it has a 7 blade cooling fan, make sure it is properly within the shroud (approx 50% of the blade in the shroud). If you are driving high speed often, you might wanna consider flaps on the shroud too that can allow radiator air to bypass the fan as with slower fan speeds the fan will become a restriction and impede airflow, hurting overall cooling. A recent High Perf Pontiac magazine did some testing with these and showed some positive results with no drawbacks.

Aftermarket radiators do well, but are often pricey. Get a LEAST a 3 core, but a 4 core is best. If you struggle finding a 4 core, the 70-81 Trans AM's had them with 455's and 301 Turbos. Probably 400's too.