On a more modern engine .020" WOULD be a huge problem. The point is that an owner needs to bring the cast bell housing AND the stamped clutch cover to the people performing the line boring. They have a pretty good idea where the front bearing should be to get the proper backlash with the cam gear. On more modern engines the rear main bearing IS centered. On these older engines that may not be the case. The bearings had enough material it could be machined to allow for variances in casting and imprecise machining practices. Without the parts that will be used with that particular engine they will center the rear line bore on the bearing itself. The service manual is quite specific in their comments about it being centered on the bell housing. Without taking those parts in and stressing to the shop that they be used as a reference, it will be a crap shoot if it will be correctly bored to line up with the transmission.
In a previous thread a fellow member said he found his to be off by almost 1/8" or .125" I think it was a running car. If no one actually checked, .020" may not even be noticed. I think he dug around in his parts and found a set that was closer. That is how much variance there can be in those parts.
Oh well, don't worry about it. It's just an old car. It'll be fine.
| 
