In "Parts to Look For" on ford-y-block.com, John said that although the 1957-59 FEK/FEH distributors have centrifugal advance, they have too much advance for performance use. He went on to recommend 1959-up distributors for performance applications. My 57 tbird tach-drive distributor is an "FEJ," which falls into the FEK/FEH category. At what performance level should the 57-59 FEK/FEH/FEJ distributors not be used? 

Not sure where all this talk about particular distributors not being suitable for performance originated from.  The L-O-M distributors come to mind as not being easily modified or suitable for performance applications but most 1957 & newer distributors can be taken apart and modified to suit specific changes to an engine.  Factory distributors are typically conservative on how fast the timing comes in so lighter springs usually helps most of those without going so far as to actually change or modify the actual amount of timing.  Some of the Ford distributors had the option of reducing the amount of mechanical advance by simply switching the lower advance plate 180° to the shorter existing slot.  Where that slot was non-existent or was still too long, then brazing or welding one of the slots and grinding/machining that slot so it was shorter would allow the engine to idle at an increased initial timing setting and keep the total timing reasonable.

The CRT/TSB distributors are ready to run out of the box.  They do come with bushings and springs similar to the MSD distributors in which to fine tune the advance curve.  I have installed several now and on stock engines with mild camshafts, the advance curve is suitable as-is.  Unlike the MSD distributors that come with the heaviest springs possible installed, the CRT/TSB distributors already have the lighter advance springs installed.  With a performance camshaft and depending upon the compression ratio of the engine, the curve itself may need to be shortened just to restore idling characteristics while limiting the total amount of advance.  That is done with a bushing change which only requires the rotor to be removed to do so.

The CRT/TSB distributors are also similar to the MSD distributors in that the mechanical curve adjustments can be made by just removing the rotor to access the mechanical curve mechanism.  Unlike the MSD distributors, the CRT/TSB distributors do come with an adjustable vacuum advance cannister so that adds another level adjustment for tuning.  Keep in mind that the vacuum advance is designed to only work during cruise situations.  At full throttle, the vacuum to the vac adv chamber is expected to drop to zero eliminating the possibility of too much total ignition timing.

Lorena, Texas (South of Waco)