So the challenge is to compose a program that works both on 83+ Basic and 68k Basic, in similar fashions. The example below clears the screen and prints "Hello World!" (This is only the body):
If sin(1)=.841470984808
ClrHome
CLRIO
Disp "Hello World!"
Edit: sin(1) is equal to .841470984808 on the 83/84+, due to it comparing only ten significant figures, but these two values are different on a CAS calc such as the TI-89. So if you have an 83/84+, the program runs ClrHome; otherwise, it runs ClrIO (the expression CLRIO is treated as the product of five variables on the 83+ but the ClrIO command on the 68k). The final line is identical for both models.

The problem is that both calcs use different token sets and prog formats so you'd still have to convert them with a comp.

Yeah true. THe best thing would be if there was some token converter somewhere that replaced ClrIO with ClrHome or vice-versa.

Also are commands on 68K calcs case-sensitive?

Well, I was ignoring tokens, and commands are not case-sensitive on the 68k.