[Top Rod]

BBC Timing question
Having a problem and looking for technical advice?
I have a 454 +.060 with Accel electronic no vac distributor. I have removed dist. and check setting on dist bench to which it is right on to manufacturer spec 24 degrees total mechanical advice starting at 800 rpm and in by 2800 rpm.
My problem is that I can not get a proper base timing of approximately 12 degrees. I have a solid roller Comp Cam with a good two summer use brass distr. gear and a true double roller Comp Cam timing chain set with again two summers time on them. I rebored the cylinders to +.060 and again this year I cant get proper timing ???
I have a Fluid Dampr and have re degreed the cam again to find it right on. When I bring #1 to TDC the pointer lines up with the timing indicator and the distributor rotor is pointing to #1, yet when I put the newly calibrated Snap On timing light I get 45 degrees as a base timing setting??
I cannot get the timing down to even 20 degrees BTC without it ready to stall? I advance the timing by ear and it starts to get lumpy and then I retard the timing and it again starts to get lump and I set it at approximately its best run & start and its at 45 degrees BTC. As I rev it I get an advance of 24 degrees on top of the 45. When I road test it it runs great and I don't hear ANY pinging!
I've been a Tech for many years and and have set many a system. A number of years ago I had the mains line bored and am woundering if the .005 or so thousands that are there would cause this timing situation? The Comp Cam double rooler timing chain set is .005 compensated from factory.
Would appreciate any help on this matter. I tried the Accel distr. in my truck 350 and it timed right on with the same timing light?
Advise appreciated. Thanks.