In the List your Set-ups thread there are at least 2 1/2A Pathfinders (Andy Borgogna's & mine) with power systems that would be outstanding in the Pinto. I used the PF to prove-out the Brodak EPS-10 power package, Andy took a similar starting point and added a KR timer. I am also using this system on a Wee Duper Zilch OTS (251 sq in) and it is great there too.
As Dennis T said, you should be able to put the battery where the tank would have gone. On the WDZ I use a top hatch, with the ESC exposed on the bottom of the fuse. Had to notch out the wing LE because of the short nose but the balance is good. I would use a top hatch on the Pinto too; its very convenient.
BTW, if Pinto doesn't have one already, make sure you modify it for a 3" bellcrank.