I have been running the Hobbywing 4274 and it measures as it says on the tin 74mm long and i have about 3mm space from the steering parts.
The mount is different on the 1.5r it is all ali without the cut out. best thing to do is measure the space you have got it looks from the pics that the 1.5 you have has the revised top plate which pulls the steering parts forward a bit.
As far as chassis flex yep even with the ali supports it will flex. Some drivers like a bit of chassis flex some do not. if you want to get rid of the flex check out
http://www.diggitydesigns.com/D3_Cas...UpperDeck.html
I have this on one of my cars and it is ace at stiffening the whole thing up and looks the dogs
As far as lubing drive shaft CVDs with boots, i have been using spray grease which is quite light but like you say if dirt gets in can form a nice grinding paste and kill the drives.