Proper Timing Technique '60 BN7

[RDKeysor]

I've decided to check the timing on my car (identified above) to insure that isn't a factor in the warm running condition I have been combatting. This car has been converted to negative ground and has a Pertronix electronic point system installed by the PO. I installed a similar unit plus a new coil on my since-sold Jag MK2, and the instructions required that the timing be reset--and I used my local Jag mechanic. I now own an older timing light that has a wire that connects to the No. 1 plug and a second that then goes into the No. 1 plug connector. Norman Nock's book (p. 88) specifies a setting of 5 degrees before TDC (5/16" on the pulley) for this car. Question, when checking the timing with a warm engine, should both ends of the vacuum advance be exposed and plugged? With the distributor bolt loose and the light steady at the 5 degree TDC location, is there further adjustment to be made? Of all the Healey books and on line resources at my command, I haven't found an explanation of this simple procedure. Thanks for any help!