needforspeed

Newbie here just trying to sort out the gremlins in my 73 240 that the PO installed a 350 SBC and T-5 into. One of the first items of business is to upgrade the battery from a well worn Suburu one that was in the car when I purchased it. Have tried my best to pull from different posts here on Hybrid Z but still not clear on what combo to use regarding the physical sizing and securing using the stock setup. I have the original passenger side tray (which is in remarkably good shape) and I need input into what battery best fits in the stock area and if other owners suggest buying the battery tray to mount under it. I also need to determine how best to secure the battery without having to drill holes or add mounting tabs to the stock setup if at all possible. So in a nutshell, compression is in the 8's and I will be running minimal accessories (electric fan and occasional radio when parked (radio will be added in distant future. I am currently still have the amp meter setup that she came with but might go to a volt meter on the suggestion of a seasoned gear-head I know. Need to know: 1. Best size battery that fits in stock setup 2. Securing options including whether the short battery tray is a good addition while still allowing good 3. Should I go with gel style to avoid having to worry about leakage onto my very good condition factory tray and inner fenderwell? 4. Brand suggestions seem to be covered in this post but if there is an advantage due to a shape in the fit or securing department, please share. Proper fit and performance are paramount so I am willing to spend more money if that will help keep keep me driving rather than pushing. Would like to spend less than $150 but would consider a bit more if there is a notable advantage to the additional investment. Thanks in advance for your input....