You can use the old bypass filter ONLY if you convert the engine oiling system to a bypass setup by moving the small plunger/plug in the left side of the block near the oil galley. (search on the subject for the details, Cosmo will have some thoughts also).
If you already have it setup for full flow then you must have a filter with large enough lines and that flows enough to allow the "full flow" of oil to pass and then go to the engine. To use the old bypass filter on the full flow setup would starve the engine for oil very quickly.
Grigg
