273 Mystery Motor

Just over 4 years ago I purchased a 1965 Barracuda that is a very clean Tucson car. It was advertised as having a Commando motor. I was suspicious of that, but the price was right and it's been a very fun 4 speed driver. Last fall I took it to a good Mopar shop here in Green Bay for a valve adjustment. They told me it had hydraulic lifters, of course raising questions. A few miles later the valve train became noisy, raising even more questions. They suspect the cam has a flat lobe and in a few weeks they are going to install a new cam. I'd like to have one in mind, but first:

1. I've recently read all 273's (including the 180hp 2BBL) had solid lifters. Is that true? If so, someone replaced them with hydraulic.
2. The motor has been modified in at least the following ways:
Offenhauser 360 single plane aluminum intake
Open element air cleaner
Quadrajet carb from 1989. I believe all q-jets from this era were 800 CFM which seems like a lot for the displacement
3. The block stamping on the pad below the head reads B273 11-19 which I think makes it a 66 motor.
4. The VIN tag decodes to a September 30 build date, which makes this a replacement motor, correct?
5. The VIN tag also decodes to the 180 hp 2BBL but if it a replacement, who knows?
6. The motor runs really really well but seems to run out of steam over 4,000 rpm, just when I thought it would be coming on cam.

My limited research indicates the Isky E-4 cam would be a good choice, or perhaps a stock 340 cam. Any thoughts on any of this? My primary goal is to select the right cam but any other thoughts are welcome. I know I should get a borescope and look at the pistons and I will do that.

You need to verify the hydraulic cam. Most shops do not know what a solid cam is, let alone how to adjust the rockers hot and running. Did they adjust the rockers for .013 on intake and .021 on exhaust? Offy makes a nice intake and the Q-Jet carb is fine. It has an adjustable secondary air valve that lets it work with smaller engines. 2 barrel pistons are good in a 273, no need for the 10.5 Commando pistons. The E-4 Isky will also run very well with your combination. A friend had a 273 put together with 2 barrel pistons, E-4 cam, factory intake and AFB that dynoed 265 hp. Supposedly 10 hp less than a factory 340. You also have the advantage of a 4 speed. Low rpm is probably a function weak valve springs, ignition, and/or Cam?