Welcome to the forum.

There is quite a bit of info in the archives on the 603 engine in the 350 SDL.

In summary, some members have the vehicle and they love it.

Others have owned it and have suffered bent connecting rods. This then requires a replacement of the block to the tune of about $8,000.

So, it's a bit of a roll of the dice. If the rods stay together, it's a fine vehicle. If they don't, and you will not know they they don't until the damage is done, then you are looking at a serious expense.

The smaller 3.0 engine in the '86-'87 SDL does have issues with cracking of cylinder heads in the early versions of the casting. Again, some crack, some don't. The cost to replace one, however, is much less than replacing the entire 3.5 engine in the 350 SDL.

You can read all about the 603 engine in the 350 SDL. Do a search with the title "rod bender". You will need a couple of hours to enjoy it all. It isn't pretty.