If you're doing the work yourself, change the head gasket and check oil consumption. If you can live with it, good for you. If not, you have the practice you need to drop a 3.0 603 block in place

You have to be in a real hurry to need more than a 3.0 603. It didn't take me long to get used to lazy starts with the 3.0. And when going fast matters, I'd rather have the free reving 3.0 over the asthamtic-beyond-4000-rpm 3.5.

As you say, it's about money. A 606 is about $4000. A 3.0 603 long block can go for as little as $500 if you have time to look (a new head gasket will buy some time). On the other hand it's about the same amount of work. What would you rather end up with for the effort?

If that's a 140 in your avatar, good luck with the topmost couple of transmission-to-block bolts. They're a b!tch and a half with the starter cable conduit and the overhanging firewall. Still less work than pulling the tranny.

Sixto
87 300D