You are correct in where you start your flow (by the oil filter on top of the head) 5/8 Tee. And where you return the flow ( by the alternator) 3/4 Tee. Use Brass Tees.
The routing should be in the opposite direction as the fuel flow. (hot water one way, fuel the other way). That gives you the best heat transfer.
I'd go:
Filter
Heat exchanger
HIH
Tank
Back to return
Have Fun

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'82 Diesel Westy
'83 Euro 300TD
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