You're asking for to much.
Let's assume you want an OD transmission because otherwise there's no point in taking out a good SM420.
The T5 is one option for a 5 speed OD, research and read about what's necessary to swap it, it does bolt straight to the bellhousing.
A larger more robust 5 speed OD is the NV4500 which can also be made to fit without unreasonable troubles.
