Yes, they all are interchangeable but what I can see from the pictures that is a Mark 1 engine = less HP than your power major's Mark 2 or 3...
Essex Lily - Super Major -62 (No. 1618924)
Mr Fordson - Super Dexta -64(dad's)
"Si is est non infractus , effrego is quod animadverto si vos can redintegro is!"
<Ut simplex, validus quod constanter ut ferrum talea campester = Super Major>
The mark I is about 38 HP. The mark II about 43 and the power has slightly more and the super has again a bit more. They ended up with the NP super around 55 Hp if I’m correct.
I see, 38 would probably be too underpowered for what we use it for. Every site i look at, seems to quote different horse power numbers for the fordson range, most confusing.