Booting BBB with old kernel


I have a classic Beaglebone running in my application. Now I’m wondering if I could plug in a BBB instead without too much headache. The problem is, that there is a lot of custom hardware around the bone, so I need to stick with the pin configuration on the expansion header as is (I’m using McASP, SPI and GPIOs). I made quite some effort to adapt the kernel for my needs, so ideally I would like to simply use the sd card from the old bone to boot the BBB - however, I figure that this won’t work.

Can anyone suggest a simple way to get the old system running on the BBB (I’m even willing to give up HDMI and maybe even eMMC functionality)?

Any suggestions are highly appreciated!