I'd check you've got a healthy spark kicking it over with kill switch set to run. Does sound electrical with it being connected with touching switch.

I'd say the pressure noise would be the plug igniting fuel in cylinder, noticed on my dtr it would produce a weak spark couple times after kill switch was set to off.

Is the clutch hub and basket lined up correctly seem to remember you can fit the dt one 4 different ways but will only work in one position

Hard to tell in the pic but looks like the gudgeon pin circlip is missing? Unless you took it out before pic.

Looks like your missing a bolt from the crank cases near inlet though.

Pretty sure there different where the oil pump mounts no?

From experience it tends to be running too lean that kills two strokes. Though a 2 stroke makes more power the leaner it runs. At 57mm you often have to modify the power valve for clearance. And the head gasket will need opening up. When the barrel 1st seized they might have replaced it with a 'good' second hand barrel that had already been taken out a few sizes.

@gilerasc125 at 57mm bore it could well be catching powervalve and/or head gasket. I'd whip the powervalve out and check for any witness marks.