1000CCA batteries weren't common back in the Eisenhower and Kennedy years, so I doubt you'd
need all that amperage. Common Group 24 & 27 (measure your tray) are typically more powerful than back then, too. Your Perkins may see similar starting (compression) resistance as a 6.6L or so V8 diesel, depending on starter/flywheel gear ratio, etc. and what works for them ought to work for the M65.
AGM batteries will self-discharge more gradually than lead-acid. It's good idea to put a
floating circuit 'maintainer' or trickle charger on either type during long Winter layups. (HFT, or better) If it's been cold enough and you're plowing snow this Winter the one you're using should give you an idea of a 'worst-case scenario.' (Is it fairly new? Don't expect it to produce full label amperage if it's old enough.)
btw, AGMs typically dry up before sulfation can wreck 'em. Store any in the coolest, driest place if you pull it seasonally. Just the
opposite of NiCads, wet cells last longest if kept to full charge (~12.75v no-load)
Think of spreading the extra cost over a likely 10 yr service life as 'cheap insurance' in the long run. I doubt you'd be reproached for buying the best you can afford. :thumbsup:
You could swap in another car battery if you sell the Massey later & put the better one in something you keep.
