Look for any post by Thomaspin and check his website referenced in his sig line. He has documented the process.
You can use a generic c-clamp type valve spring compressor once the heads are off the car. Most auto parts store rent or lend this tool. Kragen has it for $6/day. If you're working on the heads in the car, the kind of valve spring compressor that hooks on the cam is cheap enough to buy rather than rent.
78 450SEL (sold)