You have a DIY car. If you are that concerned with the timing, check it yourself.

Rotate the engine by hand till the timing mark on the crank pulley lines up with the mark on the timing belt cover. Then remove the distributor cap, and check if the rotor lines up with the scribe mark on the distributor rim. Pull back (or remove) the upper timing belt cover and check that the cam mark is in line with the mark on the rear cover.

http://www.brickboard.com/FAQ/700-900/B230FTimingBeltAlignment.htm

As the spark cables have been replaced, it may be that the distributor cap needs changing. It tends to be susceptible to humidity. When you're having problems, pop it off, wipe it, maybe spray it with WD40, then check to see it the problem is gone.
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1980 245 Canadian B21A with SU carb, M46 trans, 3:31 dif, in Brampton, Ont.