I have the Odyssey PC925 mounted on its side in the original place behind the driver , it was too tall to sit upright.
Good batteries are heavy thingies especially in a very hyper car. And for what it is worth, batteries are supposed to be installed behind the passenger to compensate for weight imbalance when driving a Morgan alone or with a less heavier-than-wife. The heavish Odyssey 925 is 26lbs (in American lingo) or 12 kilos. To calculate its effect, we must double that for 24 kilos as we are moving the battery from its proper psiition (-12kl) to the other side +12kl) . 24/460 is 5% of the rear weight of a later heavier trad! That will affect handling and suspension over the life of the car. It is the reason, so many cars sag on the driver's side. Trads were not designed for LHD driving in mind. But they can be sorted.
Solution for the battery:
1. swap the battery to the passenger's side. close to and in front of the axle.
https://www.gomog.com/allmorgan/overriders.html#3 In all cases I have seen on LHDs, the battery tray tabs are already there.
2. Find a trad-besotted wife who matches your weight plus that of the battery.
There is nothing wrong with Odysseys in other cars, (though I do not favour glass packs any more.) Do not let them drain too much and do not travel with out a trickle charger.

Yet any good solid normal battery will do the trick. And don't try to find an Odyessy in Brindisi or Bristol on a Sunday.Spend the money you save on a better placement and easier access.
Americans are luckier. Walmart sells Odysseys. However, I have not confirmed which models. Bosch is the most reliable battery in UK/Europe (duh!) and found everywhere
L.