I was wondering if the power/performance of these two engines are similar based in this specs:

OS 65AX
Weight Without Muffler: 17.5oz (497g)
Output: 1.73 HP @ 16,000 RPM

Thunder Tiger F-914 4-stroke
Weight: 26.20oz (742.8g) without muffler
Output: 1.6 HP @ 11,000 rpm

Long story short I am building a Seagull Texan T6-A and I have these two engines lying around, as per the manufacturer, the engine to be used should be a .75-.91 2 stroke or .91-1.00 4 stroke. My concern is based in the HP of these two engines, it looks like the OS 65ax is having a little bit more power and is also lighter than the .91 4stroke, but somebody told me the 4stroke engine have more torque, so that is why my dilemma beyond the scale look.

I'd go with the four stroke for the ability to turn a larger diameter prop than the .65. Plus on a warbird, you'll probably need all the nose weight you can get for balancing anyway.