Identifying "low compression" 2.1 pistons

[cobblers]

A friend of mine has a surplus recently rebuilt 2.1 DJ engine that I was planning on buying and fitting to my Syncro. My friend had it on the shelf as a spare, but he's sold his 2.1 van so it's no use to him anymore.

It was built by a friend of a friend - a guy who builds a lot of air cooled race engines (IIRC John in Stoke, if that means anything to anyone!) It's had new pistons and barrels etc, but I'm aware that a lot of the 2.1 piston kits are actually for an MV and not the spicy 10.5+ compression we'd hope for. 
Are there any identifying marks I could see with a borescope down a plughole to check before buying? The van isn't exactly fast to start with, and the engine in it is pretty much fine so I'm pretty wary of spending a couple of days swapping the engine only to lose 15/20bhp!


 

[DoubleOSeven]

[cobblers]

Thanks that's great. Looks like my best bet is going to be the depth of the valve cutouts vs the overall dish.

[Oren Kipnis]

We use "MV" pistons on any DJ rebuilt in Israel since the 80s without any problem.

The engines, although losing 10% in power and torque became much more reliable in the long term.

For the long run, I would not hesitate to install such engine.