Here is the Chinese one that is 70mm.
Professional Products 54151 - Professional Products EFI Intake Elbow Adapters - Overview - SummitRacing.com
And the not Chinese one that is 75mm. BKK and Edelbrock also make them.
Trick Flow Specialties TFS-5150SN95 - Trick Flow® SN95 Throttle Body Adapters - Overview - SummitRacing.com
The only truly effective way to lower the compression ratio is to change the pistons. Everything else doesn't make enough difference to be worth it. I would just leave it the way it is, or if you are dying to get more power out of it, throw the nitrous at it. If you boost that big 408, be ready to drop about $6K on a transmission, and $2K on a rear end.
Kurt
Professional Products 54151 - Professional Products EFI Intake Elbow Adapters - Overview - SummitRacing.com
And the not Chinese one that is 75mm. BKK and Edelbrock also make them.
Trick Flow Specialties TFS-5150SN95 - Trick Flow® SN95 Throttle Body Adapters - Overview - SummitRacing.com
The only truly effective way to lower the compression ratio is to change the pistons. Everything else doesn't make enough difference to be worth it. I would just leave it the way it is, or if you are dying to get more power out of it, throw the nitrous at it. If you boost that big 408, be ready to drop about $6K on a transmission, and $2K on a rear end.
Kurt