If that's the original cowling striping, it's a 1972, non-power-ported 1400. There was a later model of 140hp but it would look different from this one.
Pretty difficult to check compression without a starter. The best you could do in that case would be to remove the upper cowling support (over the flywheel), wrap the emergency pull-start rope (contained in the front faceplate) around the flywheel, and pull over the flywheel by hand.
As you pull it over, you should feel the resistance of each cylinder. After pulling over a few times, try to get a feel for how much each cylinder "kicks". If you have a very low or "dead" cylinder, you're gonna feel some "flat spots" as you're pulling over.
The next thing, if you're really dedicated to it, would be to remove all spark plugs and do a compression check, roping-over the flywheel. It'll take a while, since you need to give a pretty stout pull, and repeat until the compression reading on that particular cylinder stops rising.
While not being as accurate as using the starter (not an option in this case), at least you're treating each cylinder approx the same, and the compression readings (no matter what value they have) should be somewhat even with each other.
If you see a reading that's drastically lower than the others, likely there is a problem in that cylinder. The most common cylinders to have piston/ring issues in an Inline Six are #1 and #3, so pay particular attention to the compression values in those cyls.
IMHO, I wouldn't pay a premium price for a motor you couldn't run. There may be other mechanical issues (such as bad crank bearings) that would never show when roping-over.
That being said, you may find a Diamond in the Rough, just by knowing what to look for and being in a good bargaining position.
The starter is a relatively easy fix, lots of 'em available and can be changed with normal hand tools.
HTH & G'luck with the prospective purchase.........ed