Your engineer friend can easily do it. I'd suggest the Bafang BBS02 mid drive, but I don't know if your Sirius bottom bracket is a standard type. Most are though. As an e-bike conversion, the Sirius is great. Many of us convert bikes that aren't half as nice as yours. It's all about usage though. I don't ride my bikes at 30 mph. I ride them at bike speeds. And as an engineer myself, I insist that everything works.
With a mid-drive, you will lose the three speed derailleur up front, and only have the six speed derailleur in back. This is plenty given that the motor will more than double/triple any power you contribute. Set a Bafang up for 9 level pedal assist, and there should be a pedal assist level that matches your preferred biking speed. You have to order the optional hydraulic brake levers which have an electrical switch to shut off the motor when the brakes are engaged. It also features a throttle. Motor/battery should be a little over $1000.
Tools required are a $10 crank puller and a $6 chain breaker. You might want the special wrench used to tighten up the BBS02 fasteners ...$20.
The other mid drive candidate is the Tong Sheng TDSZ2. It features torque sensor on the pedals. Never seen one, so can't say anything about it.
If money is tight, hub motors are less money. Maybe $100-150 less. You cannot use a front drive,, as the Sirius has carbon forks. A 500w geared motor would be my choice for a recreational bike rider.
I own more than a few ebike conversions, one of them being a Bafang BBS02 and 250W-500W geared rear motors. Probably a half dozen batteries too.