In reading the discussion a thought popped into my head. It seems there should be a class somewhere between 3mph or 3.5mph and open (no speed limit) for NATPA. I find the comment about "I pull the open class because it is easier than the stock" very interesting. Guys have strong tractors, yes, but perhaps would like to compete in a faster speed limit class but not open ended. Get my drift? This might free up the stock classes for more stock type tractors.
This is one of those beating a dead horse kind of discussions. We can talk all day about what casting numbers are legal and what is fair but it just complicates things and the tech checks become tedious. Tunica and the USAP really have the best rules dialed in to address stock vs. modified and what engine components are allowed. Basically if it bolts up, run it. Pick your speed limit class and lets go. The 3mph stock class has restrictions on tire size & cut and tractor weight, so even fresh off the farm guys can compete. We had a guy on a bone stock Ford 800 win the 4000lb 3mph class last spring against some regular pullers. Most folks who bolt a 403 in a UB, 310 in a 77, Gleaner in a WC, etc. like to compete in the faster classes anyway and it keeps the cubic dollars required lower. It also makes for a better pull since nobody likes to stall out in 1st gear. Most guys who have more power run bigger tires anyway that put them in the faster classes. My take on it anyway.
PS - Poking fun - no problem with the Deere power blocks. They need all the help they can get to catch up. :)