No. They are not the same scale.
40K is chibi scale:
Perfect match for your alternative
40K tanks in terms of proportions... (that may actually be the one that I have seen used before too).
Anyway,
40K is so messed up when it comes to any sort of scale, you might as well forgetaboutit.
Your best bet is to go ahead and find something that is roughly the right size in terms of foot print, throw away anything that people would touch (weapons, hatches, tools) and pick up some schedule 40 pipe to fit it with some guns...
Or use some bits and smaller tubing...but a bit of schedule 40 is pretty close for a lot of them too.