I hooked up the dtr of the 8251 to the dsr of the rs232 and that seemed to help with the flow control issues since it should only send data when the device is ready.
Code
m_uart->dtr_handler().set(FUNC(apple_imagewriter_printer_device::dtr_handler));

...

void dtr_handler(uint8_t data) 
{
	output_dsr(data);
}

Giving print shop a try, looks like I need to adjust the margins a little.

[Linked Image from i.imgur.com]