One thing to consider is that although the stock speakers sound like an AM
radio - they are very efficient. For the same amount of amp power most
replacement speakers will be noticeably quieter. Not that big a deal if you
have an external amp or high powered head. But, most common ground older
heads only had a few watts of power. I replaced my stock 4" speakers in the
rear AC unit of my 85 westy with Blaupunkt 6 1/2" speakers (required some
cutting and adapter plates made from wood) and they sound much better but
at highway speeds I need to turn the volume up so much the amp starts to
distort and the sound quality gets all frogged up. This is even after I
have soundproofed the van. Had to purchase an external amp to put up in the
AC cabinet to power them (haven't installed it yet).