The 4 - 8 ohm drivers, when wired series/parallel will return you to 8 ohms. Your amp needs a minimum of 4 to run properly and not overheat. 8 is higher so it will offer the amp plenty of resistance so as to not let it work too hard. Think of it like this: The amp needs a certain amount of resistance so that it doesn't "let out" too much power. Something has to hold that power back or it will overheat.
OK, you've got your Marshal head. But surely you must have seen people using a Marshal single stack (one speaker cabinet with four speakers in it) as well as the more popular Double Stack (two speaker cabinets with four speakers in each cabinet).
When you add a double stack to your head, the total is 4 ohms. Two 8 ohm single stacks in parallel.
The 4 ohms is not the ideal impedance rating, it is the minimum impedance rating. You can't go below 4 ohms, though likely an amp like a Marshal would tolerate it.
As far as wiring your speaker. You make two separate gangs of speakers of two speakers each, then you wire those two gangs together into the final speaker combination.
There are two way of doing this-
1.) Wire two speakers in parallel, then wire the other two speakers in parallel, then finally connect these two gangs of speakers together in series.
2.) Wire two speakers in SERIES, then the other two speakers in series, then finally connect these two gangs of speakers in parallel.
Either way the total is 8 ohms.
Two 8 ohm speaker wired in series = 16 ohms, but then you put two gangs of these in parallel, it drops down to 8 ohms total.
Two 8 ohm speakers wired in parallel = 4 ohms, but then you put two gangs in series, and the total becomes 8 ohms.
The rating is not "the best match". The best match for power transfer means the load should be the sme impedance as the output impedance of the amp but this does NOT apply to solid state amps as they have a very low output impedance (a fraction of an ohm) and loading them this much would damage them.
In my opinion, 8 ohms IS the best match for your amp unless you are starving for that last watt.
I agree, you are too obsessed with 4 ohms. Right now you are going to start out with a single stack, but somewhere down the road, you are going to want a double stack and you aren't going to be able to do it because your existing stack will already be at the bottom limit.
Start with an 8 ohm stack now, so that later when you add another and still be within the limits of the amps.
The 4 ohm rating is not the ideal or preferred, it is the minimum recommended.
Now, if you are absolutely sure that you will never ever add more speakers to your Marshal head, then, yes, you can wire four 16 ohm speakers in parallel and have a total of 4 ohms. But again, you must remember that puts you at the limit of your amp. If you add more speakers, you will go below the rated minimum limit of the amp, and possible the amp will shut down or be damaged. Though I confess most guitar amps are very rugged and can handle a lot of abuse, both electrical and physical.
I'll sketch up a wiring drawing for an 8 ohms cabinet and post it later.