Fitting stick shaped lipos into old chassis can be a bit of a pain . The reason is that the most common pack around , the Yeah Racing 3200 is 138 mm long , which is 2-4 mm too long for old chassis.
here is how i modified my M02 to fit lipos, it should also work with the M01 since its the same chassis with a different engine position.
all you need is :
2x 12x3mm countersunk tapping screws (Part 50581)
4x 3mm washers (Part 50586)