There are loads of options for you. I have swapped units in loads of speakers and built my own etc, so happy to give advice.
Nowadays the smallest car speaker you tend to find would be 4". 3.5" ones are available but are less common. However if you look for HIFI speakers you can get them in whatever size you want. 2", 2.5", 3" etc...
Your problem will be the crossovers. You need to stop the lower frequencies going to the mid-range and the tweeters. The current speakers will have capacitors on the back to filter the lower frequencies out. You could try to reuse these on the new speakers but it can be hard to get right.
Personally I would replace the 3.5" woofer with a modern all in one speaker and disconnect the mid-range and tweeters but leave them in place for looks. Perhaps something like these below;
Bass Face 3.5" Inch Inch 8cm 80mm 200w Coaxial Two Way Pair Car Door Dash Shelf | eBay
You would need to have a look at the depth available in the speakers. The tweeter will stick out a bit, I am not sure you have the clearance under the grill. Depth behind may be an issue as well.
Those speakers are will not up to much by modern standards, but a bit off effort could get them sounding good. You would need a decent amp and don't expect any bass from those, but there is no reason why they could not be a decent, clear speaker with a bit of money spent.