With the height of the suspension, lots of things could have happened. It may be the original leaf springs jacked up or something entirely different from a different vehicle. But as you say, the priority is to get it going reasonably well.
Again I know it sounds silly but have you checked that the brakes are releasing properly ? They would get hot if that was the case therefore you would smell them so I think it is unlikely but it would only take a little drag to hold everything back. Just an idea. You have had the engine out so I presume that has been checked and is giving the proper power and if so then something is robbing you of the power and causing excess fuel consumption. Just trying to think of what else before you go into changing lots of things.
Having seen the driving area, it looks as though the engine cover has taken space from the accelerator side of the pedals so that maybe the reason for changing from the original pedal box. My thought was that a mk1/mk2 pedal box with the clutch pedal would be the easiest to fit but looking at it now than the orginal type may no longer fit. In which case any pedal box with a clutch pedal will mean it is offset to the left more than you might like.
And I understand the lack of heater as it should go where the engine cover has been made. But I think for a 1966/67 there should be some air vents on the top suface of the dash. From what I can see it is possible that they could be covered over so if you want to move the air around then have a look from underneath the dash. If there are vents then you could connect up some sort of fan.
Doug