Hello Bob in New Zealand, Welcome !
I have never used a 16C version, I have used a 16F84 however. The biggest thing I see is 16F628A has comparators on PortA, turn them off with CMCON = 7 . As fas as using INTOSC or XTAL, or a Resonator, depends upon how critical your timing needs are, if you are using serial outs you may not want to use INTOSC.
look at these threads:
http://www.picbasic.co.uk/forum/showthread.php?t=543
http://www.picbasic.co.uk/forum/showthread.php?t=561
JS