I'm one of those "guys from Nj"* who runs the entire MARRS series. I routinely make the 400+ mile round trip tow when I could be racing places much closer to home (and, at 8.5 MPG @ $3.45/gallon, much cheaper). I have for the last five years - in fact, when I built this car it was specifically with the MARRS SSM series in mind.
Remember way back in the hoary olden days, before SM went National? Back when the GCR included the phrase "low cost, affordable racing"? When SM went Big Time, and certainly before then, there were many in the class who were natural tinkerers. People who wanted to do the sort of development that included the sort of minutia Mike described above, about knowing that "(i)n the 1.6 Miata, there are 2 cranks. 3 blocks, 4 different head castings, 3 different 'sets' of cams, 3 different valve springs. 6 different water pumps" and no doubt investing the time and money to find out which of those combinations works best. I applaud Mike for doing so. Back then (read the archives) there were long investigations into things like exhaust systems, spark plugs, and wires, in which countless dyno hour$$$$$$ were invested finding that last 0.002 horsepower, that last inch-pound of torque. All that stuff is wonderful and valuable, but for many of us, completely at odds with what that now gone phrase from the GCR said the class was supposed to be. For many, we just don't have the inclination, or the time, skill, or money to do so. That "low cost" part is what drew many in. It brought me back from IT.
So the "founding fathers" of the class like Jim Thill and others eliminated much of the guesswork involved in putting together a reliable package. Things like spark plugs and wires were spec'd. The exhaust system was spec'd. The class even tried a spec camber allowance for a few years. In short, much of the expense of "development time" for the car was curtailed. A program was put in place to dyno and seal the engines.
I raced my first season in MARRS (and several seasons in EMRA before that) with a 280,000 mile old engine. It had great compression and leakdown numbers, never leaked a drop and was not the only reason I wasn't standing on the podium. Are pro built motors in the class? Yes, but not at the level it is on a national level. I have a pro-built motor in my car - I got it from Ed York through Mike. It's beginning its fourth season now. The leakdown numbers are good, it burns no oil, and still dynos and seals well. Why did I buy a motor instead of building one? Because at the price Mike/Ed was charging for building, installing, dynoing and sealing the thing, it was way more cost effective than doing it myself. In my case, by paying for somebody else's labor and expertise, I got an engine that I knew was going to be right (as in running, not spewing fluids or any of a 1000 other typical maladies experienced by the occasional home builder) and I wasn't going to be risking time and money (Remember that 400 mile tow, plus an entry fee?) to get to the track and start having problems caused by my own lack of knowledge. Besides, my wife gave it to me for my birthday. Are pro-built motors going to be built to maximize their potential within the spec by creating as broad a power band as possible? Of course.
The reality is that in any "spec" class there is going to be development dollars required, perhaps more so than in a more open class like IT. Face it, racing costs money, no matter where you race. At least in SSM some of the variables are controlled, to at least eliminate some of that cost. I can take my money and throw it at the driver variable in the equation instead.
The MARRS SSM program seems to be working - we've had consistently larger fields than the SM crowd has had over the years, and I would put the talent at the front of our field up against anyone else. I'd bet, given equal cars, that somebody like Mnsr. Obadia could have given Danny and the rest of that crowd a run for their money at the recent National. Come on down and give it a try - I'll even tell you the shortcuts from scenic Enn Jay down to Summit to avoid the traffic...
EDIT - You mentioned that the engine rule is your main area of interest. You cannot discount one of the other factors in our class: the tires. We still run on the "old" RA-1s. While the guys running in the top three or so are certainly going to be on fresh 1/32nd or 2/32 shaves every weekend, you can be confident that the bulk of the top 10 or 15 is not. You can still be reasonably competitive on Toyos with a whole buncha heat cycles on 'em. Last year I managed to run top 10s on tires that were well into the 30 or 40 heat cycle range. Did I know that I was at a competitive disadvantage? Of course, but reality sucks, and I was pleased with my finishes within that constraint. Conventional wisdom says that the Toyos are much more tolerant of the ham handed abuse that many beginning drivers hand out vs. teh Purple Crack, because the hoo-hoos are real race tires. Fark, I'd race on $59.95 Sears Allstate Specials if that were class spec, because if we're all on them there is no difference.
*DISCLAIMER - I/we are not from NJ, we just live there....