Deacon,
think you should simply be able to install 38, go to etc/multiboot.d/ inside you will find files ".item" get the older power 37:
Maemo-2.6.28.10power37.item
Open and change the line:
ITEM_KERNEL=2.6.28.10power37

Should be:
ITEM_KERNEL=2.6.28.10power38

I expect that should be all mate. You may have to use xterm and copy file to MyDocs, alter and save back depending on how you do it. Would be something like:
cp /etc/multiboot.d/Maemo-2.6.28.10power37.item /home/user/MyDocs/
cp /home/user/MyDocs/Maemo-2.6.28.10power37.item /etc/multiboot.d/

Hope that helps