I had new mounts but still couldn't get a new belt through there w/o loosening the mount nuts quite a bit and jacking up the engine.
Thinking I didn't want to do that on the side of the road (belts rarely break when the car is sitting in the garage) I added shims to raise the engine.
The mounts on the TR4 are round so I used big washers of the same OD and the holes were also big enough. I opened up a slot to the hole (quick work with an angle grinder), making the cut slightly angled, sort of based on the slot used on the rectangular TR3 shims:
As I recall I raised the engine 3 washers worth on each side -- a bit more than 3/16". I put a dab of Aviation form-a-gasket on the washers so they wouldn't want to squirt out (brand new metal is pretty smooth stuff).
Didn't have to remove anything, just loosened the nuts and raised the engine with a 2x6 under the oil pan & slipped the shims in. I 'clocked' the slots so they weren't all lined up.
I also raised the radiator (shimmed the lower mounts) by a similar amount to avoid straining the top hose.
Now there is enough room for an easy belt change.