Yeah, as the guys said, you'll be glad you pulled the engine/gearbox.
I've done it both ways, the first time I left the engine in place, because I thought it'd be much easier. It is very possible, but after a few hundred miles it started to weep coolant along its lower edge onto the exhaust manifold. Because the head is on an angle I never liked the fact the head rested on the side of the head studs before you torque tightened them and I never felt I'd done a thorough enough job. So a year later when I needed to replace the clutch I thought what the hell, pulled the lot out in a few hours and had another go at the head gasket at the same time. I can tell you I replaced the water pump, tensioner, belts, clutch, every bolt, cleaned and painted the engine, replaced the engine mounts, painted the chassis, replaced all the hoses and refitted the lump in the time it took me to pull & replace just the head when I left the lump in. Your back will thank you for it you'll make a better job of it and you'll get so far into it before you'll end up pulling it anyhow.