73 360 Ignition timing after Chain replacement

Hey all. I did some searching here, and found dozens of varying opinions and figures.....none of which directly answer my question.....so I am going to ask again for the often asked "what timing should I run"

Details.....Engine is a 360, casting from July 72....I believe original to a 73 tradesman body Motorhome. (installed now in 74 D300 flatbed, but that's beside the point).

I recently pulled this engine out of said 73 tradesman RV.......Had the heads done full new valves, guides, and seats. New Rod and Main bearings.

While it was apart, I also replaced the timing chain with Mopar Performance double roller. Assuming the rest of the engine was original (seemed very untouched on disassembly)......I figured stock cam, so I set the new timing gear set to the stock notches (as opposed to 4 deg. + or - options)......I am about 98% certain I lined up the marks correctly.

Now I've got the engine installed in my 74 D300 dually. It fired up okay.....but clearly Distributor timing was off a bit......I moved Disty around until it idled ok.....warmed it up and put the timing light on it.

Here's where it gets me wondering......The sticker on the valve cover, for 73 models.....specs the 360 to be timed at 2.5 BTDC with vac port plugged. I can't get it anywhere near that....stalls out around 10 BTDC runs best with timing set between approx 15 degrees BTDC.......will run all the way up to 25+ but bucks on startup that far advanced. I haven't actually driven it yet as the truck still needs some other stuff done first.....but engine seems to start and run well with timing around 15 BTDC where I left it.

I verified the TDC mark on the pulley is correct, both by comparison to another pulley, and with a wooden dowel feeling piston rise/fall through spark plug hole.

Should I be worried my Cam timing is off? (Chain installed tooth off?) Or time it to feel, listen for pinging under load and adjust accordingly? Perhaps it has an "RV" cam? I mean it was pulled from a 14" RV? I hate to pull the chain cover back off just to find I did indeed set the gears correct. Like I said I triple checked the install and am about 98% sure that the double roller, Mopar made chain is correct.

Should I be dead set on getting it timed to 2.5 BTDC? or does 15-18-20-ish BTDC sound reasonable? any risks to consider? Just trying to bounce around ideas and talk myself into or out of pulling the chain cover to verify Cam timing.

Thanks to all those more versed in LA engines than I am.