Will the tank and seat assembly from the new Continental fit on the old iron engined Bullet
If not what mods are needed?
It is an entirely different frame, so I'm sure it won't just drop on for you. The older bullet frames, in particular, are hard to fit a cafe style seat since they don't have rails running back from the tank parallel to the ground. You need to fabricate a sub-frame if you want that style seat.
There are plenty of places which can manufacture you a tank to fit, or you can buy one of many ready-made cafe tanks and modify it to fit the Enfield.
I know Glass from the Past has an Enfield-specific cafe seat/tail and will give you the plans for the sub-frame support you need to fabricate to support it.
Besides GFTP, there are Roc City, Airtech, slipstream cycleworks, Pat Cowan, Legendary, and many other places you can source bodywork such as tanks and tails. But fitting them on our bike frames is never a bolt-on proposition. There will be welding and bending and tabbing and drilling...
I had a guy named Ken Hosford make an aluminum seat for me for only $125. Can supply his contact info via PM if anyone would like to talk to him about a seat.
Indian-made products may offer a less-costly solution. Sans Classic Parts was doing a cafe package last I recall. And Indian tanks are widely available on Ebay. But it's a crap shoot with Indian stuff sometimes.