What material for Risers?

[FishStretcher]

Assuming your tank is in the stock location, and your engine weighs more like 400 lb, not 250 or less, then put all the batteries forward.

I have my 20 gallon tank and 2 batteries under the console in a 1975 20 foot master angler. I have 420 lb of outboard on the transom (100 HP 4 stroke main, 6HP 4 stroke kicker). Balance is OK that way.

If the weight is a bit too forward, remember where everyone will be when boating a fish- an aft corner. If possible, put too much weight forward. If you don't like it, put tackle or a livewell in the stern. But I don't think you will have to.