More good input, xvs. I'm going to check out the RPM situation this weekend. What kind of Elect distributor did you get? The guys at Indmar told me thay have a kit that includes a GM dist., wires, etc. that is a drop-in for ~$375.
No valve seal smoke, yet, but I do get black smoke from a rich condition when starting the engine after the engine is thoroughly warmed up and we're doing lots of stop & start with changing skiers, etc. My only thought is to change both needle & seats in the Holley. Have you had any carb issues?
Did you have any trouble finding a replacement block? I understand these are 4-bolt main blocks and finding a MarkIV (old) performance block could be difficult and would be pricey.