That's pretty much the design of the battery tray I also use with my Dynatron, except without the handy ni-starter caddy. I used some G10 fiberglass board for mine, but 1/8th plywood would also work. If using wood, I would cover the outside with epoxy/fiberglass cloth to encourage all the seams to stay together, and help protect it from the knocking around it naturally gets.
Just make the tray big enough for the battery, with room above so you can easily grip the starter and squeeze the start strip. I made mine a bit too tight, so it is hard to get the battery in and out, but since I just charge it in place anyway, it is only very rare times I need to wrestle with it. Physical length of the battery is probably the only real constraint. My battery is crazy big - 5000 mah, which is probably why it lasts all summer. You could go much less in mah (1000?) and still go a long time between charges. I'll do that if the current one ever dies. Going on 6 years though...

A123 is the original company that came up with LiFe batteries. The gold standard for them, BUT it went bankrupt several years ago and while the name is still out there, production has changed several times as various new owners bought the assets. For planes, I still ferret out the name - either original or whatever the latest is. For support equipment, since it is not critical, I'll buy whatever cheap Chinese import for LiFe I can find.