[1QuickS]

Jetting looks OK. Be sure your Webers are IDA and not IDTP1 which were OEM for 914/6. The IDTP1 Webers have a different progression circuit design from IDA Webers and behave differently at transition/cruise than IDA Webers.

Typically main jets used with F26 E-tubes are larger than when F3 tubes are used but since you soldered two top holes shut the main circuit should come on a bit earlier and possibly be a bit richer through main circuit operation. If you wanted to affect transition mixture then I suggest adjusting idle air bleed jet size, these are not typically a tune-able item but they can easily become a tuning option. They adjust progression mixture just like the main air correction jets adjust main circuit mixture...larger jet size results in leaner fuel mixture curve with advancing engine RPM and conversely.

Double check cooling air paths on you engine for heat issue: fins on cylinders, air diverter plates attached to cylinders (there was a modification for these to help cooling efficiency), thermostat operation (you have performed this but check to see it opens at 180 degrees or whatever it should do) and radiator fins of oil cooler mounted to engine. Did you have your oil cooler cleaned/flushed when building your engine? Also check distributor for timing and smoothness of operation, spark plug selection for your engine. Check air flow balance of Webers at 3000 RPM.