3 scrap cranks later... I've sent the original crank away to have all the main bearings replaced, dynamically balanced, conrods and pistons weight matched and then welded.
Decided to use one of the other blocks to try the 90 carbs on. Had to countersink the top screws on the bottom 2 carbs. Took the 165 main jets out of the 70 carbs and put them in the 90 carbs.
The throttle and choke linkages from the 70 carbs all seem to work on the 90 ones.
The throttle cam isn't perfect, rubs on the metal part of the carbs a wee bit, going to wait until it's back together and see how it goes.
Think I'm going to have to cut a hole in the tray for the bigger bowls on the carbs.
Also put the CCM reeds on this one, removed the stops as well.