Doh!! on ME!!
My post was about a 360 not a 340. My brain got crossed up for a sec there.
The same rule still applies to the 340.
On an internal balance 340, just knock off the converter weights and bolt it together.
On your cast 340, You could use your flexplate and the weights from your 340 converter.
After knocking the magnum weights off, weld the 340 weights onto the same spot on the a518 converter relative to that offset lug.
The B/M balanced flexplate for the cast crank 340 is the other alternative. You will still need to knock the magnum weights off the converter tho. Just the biguns. The little thinner postage size ones, if there are any, need to stay.
2. The reinforcement looks good, but I can't give it a complete thumbs up without being there, I can't tell how well he connected the new work thru the floor to the xmember.
The floor skin is only spot welded to the Xmember so the welds have to go all the way thru or they are just laying on the top of the skin.
Did he weld the reinforcing pipe thru the xmember?