The Giant may work - but they're known to have... well "giant" Dtubes and this may make installation difficult. If you have the room then it can be done - pics would help us
I've been considering a pull start modification myself so I can start my bike in the mornin' to warm up without pedaling halfway across the yard heh - but they might compound installation problems as your pedalcrank might
hit the recoil housing. *shrug* not a huge deal - you could get a different crank arm or remove the recoil and put a plain cover on it, or you could get a regular pedal start and upgrade to recoil later, they're only $20.
Although Grubee kits tend to have slightly better parts included with the kit, it's far more important to use a reputable dealer than the name stuck on these (mostly) identical engines. I would heartily recommend;
ThatsDax: bicycle engine kit, bike engine, bicycle engine, bicycle motor
Spooky Tooth: Spooky Tooth Cycles - Motorized Bicycles: Gas Powered and Electric Bikes - Home
BikeBerry: Bicycle Engine Kit - Covert any Bicycle to a Motorised Moped. 150 MPG!! Wholesale Beach Cruisers, Chopper, Mountain, Road, Tandem and BMX Freestyle Bicycles. - BikeBerry.com
Could you post a link to the last one you mentioned? The "80cc Dual Start 3 Speed Dual Brake Gas Bicycle Motor Kit"? That really sounds like a complete bike and not just an engine kit...