" I had not noticed the spark plug threads, "
____ If it's not a "heli-coil", then it's likely a 'threaded-insert' .
" Maybe I was mistaken and what I read was that there were heads that didn't have the fins on top that went all the way through? "
____ Now that's more likely the case but, that's an irrelevant detail for separating 250-head models, as the fully-threaded head-tops were discontinued along with the original square bolt-pattern of the 175/200 cyl.heads !
" Like this head the fins go all the way across "
____ Did you get 'extra' parts along with your Duke-find ?
" The engine came with no valves installed as well as the missing piston (which I believe would have helped further identify). "
____ Too-bad,, the piston should've been the 3-ring type with high dome.
" So it seems it's a 36/33mm head "
____ That would mean that the corresponding intake-port should be under 29mm !
Did you not yet measure it ?
" According to a few others on other sites those m-baruzzo torino wheels are really hard to find and were only used for a few years on the Mach1 and Mark3's, and the butted spokes are correct for just the Mark3's. "
____ Seems to be good/correct info, but I can't confirm that the lightened-type spokes were not also used on the Mach-I.
questionable source wrote: "These Diana's featured chromed steel rims by M. Baruzzo, which are really hard to find, since they were not used on too many bikes. They are very narrow, 1.6 inch wide for 2.00-2.50 tires... The Diana 250 spokes are the "high performance" variety, 3.5mm at the ends and 3.0mm in the center of the shaft."
____ I have two issues with that offered info...
First, the source is guilty of misuse/overuse of the name "Diana" ! - Thus further adding to the confusion-issue between the real 'Diana 250' & the n-c Mark-3 ! _ (I really hate that !_ [Especially when a supposed Duke-expert states that Dianas have "magnetos".] )
Second, I believe the Mk3 spokes were the same 3mm std.size at their ends and slimmed-down to 2.5mm for their main-length, (that's 3.0/2.5/3.0mm, not 3.5/3.0/3.5mm).
" I'm still quite unsure as to what my final decision will end up being as to what to do with this bike, but either way I figure it needs to be taken down to parts so that everything can be soaked and cleaned to get rid of the rust and grime and put back in properly lubed. "
____ You seem to have the makings of becoming a true 'Duker' !
Hopeful-Cheers,
-Bob