Are 340’s rare

That's almost a record. 180 post without an insult. Good read while it lasted.
I'm no professional builder but it makes sense to me that there is some advantage to air flow with a bigger bore concerning valve shrouding.
Yes but that has nothing to do with a "square bore/stroke combination"
Ford 400 basically a 4" stroke tall deck 2bbl Cleveland with big block bellhousing.
Some of the first year 400s (1971) had both big and small block bellhousing patterns.
yup...just googled it. T bird, Torino and Trucks!
And LTDs and Galaxies, and Country Squires. The 400 was a very prolific engine for Ford. It was a workhorse. I drive one sometimes every day.
This must have had a " square" engine.

Interesting, I sold a Dart that I thought had a stroker, per person who sold it to me. Well, took said car to my buyer, they drove it, was completely satisfied on how it ran, power output. Told me, "it runs very good" Well, sold the car. Get a call a few days later, seems it is not a 360 stroked, but ONLY a 340. Well, I refunded some money, it is only right, BUT they told me "if it were only a 318 I would not want it" AFTER saying how good it ran!!!!!!!!!!!! What difference the numbers on the block, they look the same.............
This is a very interesting story...seems history is being rewritten now with al the 318 hype nothing has changed with them since the 80s IMO but going forward the guys that have them will want $$$ for them now...I used to get 318/904s for the price of a tank of gas...
I've got 3 standard bore 340 blocks as extras and a couple standard bore 360s. I bought them when they could still be had reasonably.
I had a standard bore 340 block for years I just decided to build it a year or so ago. 'waiting on the heads at the machine shop now to finish it up. The are good when you have them the only guys that talk smack are the guys that don't have them.