Woo',
There is an unusual bracket the is used to mount the original speaker in place. I've never found any vendors that have them, but have seen several radios for sale on EBay that have the bracket included(pricy). I'm sure a person could come up with something similar that would work. I'm like you, having them mounted under the seat would work, but under my seat there is't much space available after I mounted the brackets and such for my jack and tire tools. Shouldn't take much imagination in the shop to bend some steel to work. That's my plan at least in order to get the original AM radio back in the dash. Good luck.
Tramp
