New here, but, I was one of the persons that was on the GM team that designed and developed the large coil in cap HEI's. I also am well versed in both large HEI's, and small-body HEI conversions, 40 plus years of them.
Easiest way to get 21/22 degrees of timing for mechanical advance for the large HEI is to use 41 weights, 375 center scroll plate. These are what comes in the GM ZZ crate engine HEI's, and a lot of later Suburban distributors, and has mostly been adopted for aftermarket HEI's. These ARE NOT the parts used in the after market curve kits sold by most, those kits eliminate the vacuum advance, and set the curve degrees to 16, for DRAG RACING use only, NOT for street use.
There are no lists, nor info on what curve is given by combination, but remember, EVERY stock curve, except the ZZ, is an EMISSIONS curve. Some of the their combinations may well work for a special performance application, but, it will take years to go through all 437 of them to find the right one.
As far as replacing a magnetic pickup in a large HEI, DO NOT JUST GET THE COIL FOR THE PICKUP, BUY THE FULL AND COMPLETELY ASSEMBLED PICKUP, their outer reluctor is already centered, and do not take it apart.. The difference in parts costs is only about a dollar, the frustration level in getting the outer reluctor reset to not hit the inner, is well worth that extra dollar. If the pickup isn't stable when its wires are moved, the pickup is defective, and when new ones do that, they are new defective, and should not be used. The issue is, where the single windings wires are attached to the stranded wires to the connector are bonded together, the bond is very weak, and failure will ensue, not long into the future. If the readings are constantly changing when the pickup and wires are let sitting with no movement, the insulation around the actual coil inside the pickup is compromised,and allowing the windings to touch each other inside the coil area, new defective pickup coil.
In testing an ignition coil, resistance values are relatively useless. They rely on a cold coil, when most large HEI coils fail when they are at operating temperatures. So, to properly test a large HEI ignition coil, take it out of the distributor, and find a good auto parts store that has an off vehicle electrical tester that will actually run the coil. Let it run to get it to operating temperatures, and see how it goes. Replace as needed.
Be aware, the epoxy filled coils in the large HEI caps do have significant failure issues, such as not leaching coil heat out of their jackets, epoxy does not conduct heat away from its source, it rejects it back into the source. When this happens, the insulation between coils degrades, the windings touch each other, causing a "layer short", which changes the loading on things like an HEI module, or MSD box internals, to failure. Ever hear this "That HEI module failed FOR NO APPARENT REASON". Well, NOTHING evr fails for no apparent reason. Lots of people have had numerous HEI module failures, and were told that it simply was not the coil that caused it. then, after washing time and money on every other part in the distributor, they finally change the last thing left, the thing they were told had no problems, ever, and, the distributor stopped killing HEI modules. Amazing.
There are simple parts available to move the coil out of the cap of the large HEI, allows the use of a remote mounted round oil filled coil away from the distributor, stops module failure issues once and for all. Also reduces the under cap temperature of the large HEI by as much as 55 deg/F. on average. MSD makes the parts needed.
As far as off idle leanness, lack of transition, both INITIAL and IDLE timing has a lot to do with it. If these settings are not correct, off idle transition and idle transfer settings will be adversely effected. One thing is to get the INITIAL timing worked out, conservatively, and supplement the IDLE timing with the full manifold vacuum sourced added timing correct, then, get the carburetor set up right. It isn't that hard to do.
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