I've done a lot of carb swapping from v8's to the chev 6 and never changed jets at least not for just that reason. OF course other stuff affects jetting like air temp, headers, etc but not number of cylinders at least in my testing. So I'd go with about a 65 primary jet and see how it runs. In the 600 Holley Ive used everything from a 62 to a 68 jet depending what the combo wants.
Agree a 600 is a bit big for your motor but (see "new guy with engine" thread, if your minimum RPM is about 2400 or more it should work okay, free is a better value than a new carb!
