How can I adjust the 5% sample of 1960 to 1%? I want to use the variable county only available in the 5% and make the sample consistent with the 1% sample.
It seems that the best way to go about this is to use the custom samples extract option before submitting your IPUMS extract. This has the benefit of adjusting the sampling weights to any sample size adjustments. Another way is to randomly drop 4/5ths of the 5% sample from 1960 in your preferred statistical software. For example, in Stata you can use the sample command.
I do wonder, however, why you want to do this in the first place. The sampling weights (e.g. PERWTand HHWT) are both useful for scaling up any sample to the full US population in any given year. Therefore, when incorporating the sampling weights any sample will be representative of the full population and comparable with each other. For more information on sampling weights, check out this blog post.