Why on earth would you want to put 1.3 in an a500+?
I'm going to be adding an ecs denise & agnus, and ks 3.something probably to my a500. 1.x is irritating me to no end. Sure I'll use a kickswitch for old games, but thats it.
Anyway 1.3s support for mass storage and drivers is awful. So if you have a HDD and/or cd-rom, don't to it!