It is normal for the resistors to get too hot to touch. That's one of the main reasons the original boards are not ideal.

I would replace them with a more modern set of aftermarket boards made by several vendors.

In stock at AU$55 the pair (that's only about US$40 for you) and greatly improved over the originals. Many buyers report delivery from Australia by ordinary air post in under two weeks:

http://www.johns-arcade.com/#!product-page/c1cs/e16af231-9f4b-6d3d-7631-be95f87ae1ed

I also advocate repair over replacement but I disagree that "older boards were better built". I repaired a WMS driver board yesterday (transistor broke off its legs) and the tracks are disgustingly small, the print quality is woeful and the plated through holes are hopeless.

Modern printed circuit boards are a massive improvement over 30 year old tech.

We have some of the best equipment available in the factory (as you might expect) and I have a lot of experience repairing these over many decades but I still cringed at having to do it and work with kid gloves - you just don't have to do this on newer PCBs and that is my point:

Newer PCBs are far and away superior in every way to 20~30 year old ones.

With that said, I certainly still advocate repair over replacement where it is practical and where the end result will be reliable. These trough boards are a well known weak point due to the continuous mechanical thumping of the balls and the (IMO) poor original design, putting large, hot resistors on a board in this position was plain silly.

In fact this original design looks like it was done by a high school hobbyist - there is no need for these large, heavy, hot resistors in the design to start with - but that's a different story, there are tens of thousands of them out there working just fine so it's not all bad!