Torque converter & flexplate??

Alright so I’m currently unsure about the flexplate and torque converter I should use with my 76 duster. We are putting in a 1970 340, bone stock so I assume OEM crank (internally balanced). The transmission is a 904 and I’m unsure about the torque converter and flexplate to use with the 340 904 combination. I looked in classic industries and they only sold flexplate a for 318 904 and 360 904 combinations so I really don’t know if the 340 is any different than those. I purchased a B&M flexplate for the 904 with a 10 inch torque converter mount. I’ll link in my possible options and if anyone can let me know any suggestions if this will work or not. Also I’m pretty sure the answer is no but would a 9.6 inch torque converter work with 10 inch flexplate. I feel like it’s a dumb question but I had to ask.

flexplate:
B&M Flexplates 10231

Torque converter:
https://www.manciniracing.com/haytwister12.html

There are two bolt patterns for torque converters..11 and 10 inch. ....the smaller converters use the 10 inch bolt pattern.

if,you scroll down the page on the converters link it tells you the bolt circle...10 inch

The b&m flexplate is for a 8 inch bolt crank.....an oem 340 crank has 6 bolts

look at 10230

search eBay you can find flex plates a lot cheaper the that b&m

I see your in Mass. I've got a new in the box SFI Mopar flex plate part #p4529751 let me know if it'll work for ya'..

Attached are the 4 flex plates used by the factory. Note the two different patterns for bolting the flex plate to the crank.
Hope this helps.

I believe a flex plate and converter from a 318-904 would work. It'd be an interesting test.