You can do well over 70hp on a stock bore stock stroke engine. Only requires high compression piston, head porting, cam, throttle body, and race fuel or e85.
As Troy says, 70HP and torque around 55FP is possible with stock bore/stock stroke. You'll at least need a 11:1 piston that is pump gas safe, or depending on your elevation maybe 11.5:1 piston, head porting by a qualified porter, cam would be a HDD5050 or Web 4 and required springs and maybe bigger valves, and a +3 bored factory throttle body. High 70HP would need 14:1 compression, bigger valves for sure and race fuel/E85. And as mentioned, SCE head gasket and studs. A 12:1 piston is available but if running race gas , might as well as do 14:1 Want more torque and more HP, do a stroker, but be ready to spend $2000 on 5mm or more stroker, trued, balanced and welded. No matter what crank you use, always have it trued and welded. On ALL my builds I like to use a "crank bearing support plate" available from Cuervo.
One thing to be aware of, 70HP can be a handful depending how tight or open your trails are.
'19 Can-Am X3, RS Turbo, 172 HP, 1300x15 STU #2 paddle, Tribute front, DynaTec controller, cat delete, GTP blow off valve, custom flame wrap, Bent Metal windshield, Blazer wiper, rear window, 48in LED light bar, 14in LED light bar, GTP LED side lights, S3 shock tower brace, aluminum rear pull plate, 5K Badlands winch, dual batteries, 5ft lighted whips, Rugged radio and intercom, interior lights, rock lights, chase lights, over $200 additional switches, YES, street legal with dirt tires.