Upgraded 360 Cam?

You mentioned a dual plane intake. Did you change intakes and how did the engine look inside? We may also need to know cylinder head casting numbers. There's some industrial/motorhome 360s with an 857 head casting that are 318 industrial heads with small ports and valves. But it may also have a set of 974 casting heads which can be made very good in their own right for the cost of a single Edelbrock head.