Any .21-.32 size engine will physically fit the mounts, and the flywheel/collet should work, but you sometimes run into problems with back plate clearance and exhaust fitment.
You could make the HPI 3.0 work, but it would be a lot of modification for no real gains. You need to be looking at other .21 size engines, or .25, .26, .28, etc if you aren't worried about complying with racing regulations. There have been some screamin' deals on the OFNA Force .28 and the Associated .28 Pro, both of which make A LOT more power than your current SH .21.
Just remember, .10 to .20 CI (1.9-3.4cc) is gonna be "small block", .21-.32 CI (3.5-5.2cc) is "big block". Generally, small blocks are for 1/12 and 1/10 scale, while the big blocks are for 1/8 or 1/7. Lots of guys shoehorn big blocks into 1/10, though, and there have been a few 1/8 cars produced with small blocks.