Dax is an extremely reputable and friendly dealer - I would recommend just givin' him a call
Grubee Starfires are one of the higher quality kits, but this is primarily about what optional accessories are included and their quality - most of the engines themselves are almost identical regardless of what they're called.
The ones from Dax aren't actually Grubee kits - but I've heard his have slightly better construction, larger wristpins & better bearings if I'm not mistaken...
In any case Dax will take care of ya - and that's a fact
Good luck with your build - sounds like you've the right idea!