7.0L EFI or 7.3L PSD for jet drive boat

The jets are un-complicated and have few moving parts. You are unlikely to need to replace the impeller as was implied a few posts ago as the grill will stop crap getting to it. You have 1 thrust bearing at the front (QJ308 in a 212, brass cage, split inner) and a rear bearing (cutlass in a 212 and cam bearing for the 'Turbine / Berkeley). Seal is a mechanical carbon seal type (Berkeley run the older rope seal). So nothing is expensive nor difficult to get to. If you are capable of fabricating your new setup, you are capable of doing the maintenance.

The American Turbine SD309/ Berkeley 12J is not going to move enough water for a boat of that mass, even the older Hamilton 773 (no such thing as a 777, they are a 770 series pump and the last number denotes the amount of stages. I do know of a custom 4 stage, but certainly have never heard of a 7 stage!) or Marine Power / Kodiak equivalent will struggle.

Not sure what the Hamilton 212 is worth there. It is well suited to the petrol motor and costs significantly less than the HJ213. The 213 is more expensive as it is a 'permanent immersion' pump, has a larger diameter main shaft and has a hydraulic pump, cooler and proportioning valve built in to run the reverse bucket.

What power are you getting out of the petrol motor? At what RPM? This will give you an idea of impeller selection required.

The petrol may consume a little more than the diesel, but maintenance costs for the diesel are greater. Also as you have discovered, the cost of a pump designed to absorb the diesel power at such a low RPM sky-rockets when compared to one designed for petrol.