we turned stock rod WKA flatheads at 7100 in 99 with zero issues, though many vented blocks with the cheap rods that people were buying.You Say older depending how old they did not turn them 7000 then.
best pipe we had was a muffled pipe made of stainless by profabOur inertia dyno showed the flathead to be sensitive to to pipe. Some big pipes made good power then fell off the table at 7k. Others were a point shy of peak power but held it and tapered off. We got to preferring these so we could gear a little shorter and get better drive off the corner. I got a skinny little weeny pipe in a box of parts from a friend and it ended up being the go to pipe for my Dover adult flatheads. Go figure the pipe I got for free worked better than the ten I bought from the top names.