Duct,
This is exactly the kind of question that I answered regularly when I did a lot of work on performance cruisers before the depression.
First, I like your choice of Lifeline AGMs.
Second, Lead/Acid (LA) batteries don't play well together. If you make up the bank of two strings, please put in switches and gonzo mama fuses.
The switches are so you can periodically charge each part of the bank to independently so as to get all the cells to full density.
The fuses are there as protection in the case that one jar shorts a cell. (This failure is very rare with AGM, but it can happen.) When this happens the good bank dumps all its available power into the shorted cell and the result is not good.
Other than that, go for it.
Matt
