I'm brand new to this forum but not brand new to TR's - I've owned my '4a since 84 (off the road since 89 in favour of a TR6 and GT6, then Porsches).
When I was about 20 I did a frame replacement. The body is not that heavy so you can get any with a 1/2 ton or greater come-along or ratchet hoist. I recall using the bonnet and seat belt mounts as anchor points to start. Once you have lifted the body up a bit, place timbers between the frame and body. Then, use ropes around the timbers at the centre of the arches to lift further.
You most likely have a cracked