I did my first 2x20 anaerobic threshold test with HR and need some help quantifying the numbers, first a little background.

Riding for two seasons, the first season on a single speed casually, last season much more seriously on a road bike(hadn't ridden a bike prior since i was probably 12 or 13 yo) .

Test was done on kreitler 4.5 dia. rollers with resistance fly wheel, new belts.

I'm 29, 5'10.5" 130+/-2lbs and I do have a weekly training regiment(indoors, winter here) that includes intervals, tempo, and endurance on the rollers with light weight training mixed in(two non-riding days).
I'm putting all the numbers so it will be easier for you to see where I'm at.

10 min warm up
#1 20min
Max HR-181
Avg HR-176
Avg mph-25.98
max mph-27.73

5 min recovery.
#2 20min
Max HR-183
Avg HR-175
Avg mph-25.48
Max mph-27.96

Mph is kept for cadence purposes since my computer doesn't have that function. My estimated cadence was ~108 at 26.5mph which is where I tried to keep my effort. I was working hard the whole time but the last 5 min were ruff, the last 2 min of #2 I almost quit, the last min I excepted the pain and that's where the max mph of 27.96 was hit.

Questions:

Is 183 my anaerobic threshold HR? If not, how would I calculate?

Is there a difference between LT and AT HR?

Note: I plan on racing this season and need a more structured way to train, also, Im getting powertap soon and I want to try to combine power and HR based training so I figured I'd get started.
This racing season will be purely learning and training. Take it slow now to go fast later.

Thank you in advance for any information that might be useful.