My present Isaac AS fork needs replacing. I have been offered a nice 853 fork with the same A-C measurement.
Head angle 72 degrees.
Isaac  43mm. offset  63 trail  19mm. flop
853   52mm. offset  57 trail   17mm flop
(according to online calculator)
Will I notice a lot of difference?
Not a good idea?
I should have mentioned road bike running 28mm. tyres
Depends. I wouldn't but some folk would.
I suspect that'll be horrible to ride with the new fork.
A longer offset can be good with a more relaxed HT angle. 53 is fairly long for a road bike and you may well notice it feeling different - lighter steering with a tad less weight on the front wheel, which might not be great. But there's riders on similar geometry who are quite happy with it.