On the later 400 series Tek scopes (and many others as well), serial numbers beginning in "1" were produced at Guernsey. I do not know if this holds true for the 453. But it is very possible that this is a Guernsey produced instrument.
"Early" s/n Scopes (019999 and below) were originally produced with NUVISTOR's and should be the only instruments equipped with these two resistors in their respective circuits.
If yours is a later model scope, then, according to the schematics. it will not have R471 or R675.
If these two resistors are present in the scope, then it was originally produced with NUVISTOR's or has an older model board installed (if this is even possible).
I am far from an expert on these scopes, but I seem to remember that there was a way to convert older models from NUVISTORS to FET's
You definitely need to make sure that your instrument and your service manual are for the correct serial number range. .
I have a 453, but it us a "High" serial numbered unit.
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Michael Lynch
Dardanelle, AR
Michael W. Lynch