Installing 1972 340 manifolds 3614368 (driver's side) and 3418623 (passenger's side, center dump) - Any Exhaust Pipe Clearance Issues to be Aware of?

My car apparently was a former race car and I'm finding things on it that don't necessarily agree with the factory service and parts manuals. For example, the current motor mount insulators (biscuits) on my car have "2265" molded into the rubber, which according to most aftermarket parts catalogs is for a slant 6 and not a 340 (P/N 2266). I suspect that the former owner installed the taller slanty biscuits in order to gain a bit more engine height for clearance for the long-tube headers that are currently on the car. I suspect that I should install the correct lower 2266 biscuits if I'm going to install the exhaust manifolds.