g3n3Ral,
I've just seen your post - belatedly! I have to say that putting a 4 stroke in is much MUCH easier before you even attach the rear part of the fuse' to the front - and certainly before you sheet the front.

I've ended up, as you would expect, with cutting away some of the firewall and the fuel box. The tank will project at least 2 cm beyond the box rear [i didnt glue the tank box end on as per suggestions on the 'thrust angle' thread. A 70 is a big beast for this plane. Are you happyb that it will fit between the engine bearers and that, when the mounting holes are drilled you will be able to tighten the bolts up? My view is that, B4 you sheet the front, you should have installed, or at least planned:
- position of all servos, rec. battery and receiver.
- throttle linkage
- run of fule line including where the filter will be and how you will fill it up [I have used a Du-Bro gismo so that I can fill from the side of the fuse' without taking any fuel line off.
- work out the run of cables to rudder and elevators.
I'm mounting all radio gear jsut behind the fireall so I dont have to add weighs to get the CoG correct.
Fuel tank goes in the box but will project out. Short run of tubing up to the carb and you will need to blank the third hole off permanently unless you plan to fill via it and blank off after each filling.
Dont forget to work out your run along the fuse for the receiver wire and install a tube

Read and re-read the 'thrust angle' thread - the posters certainly know their onions and it will save you grief squared. there is also an excellent dutch thread on a flair pup build with some good photos - hope you speak the lingo.

Re your questions:
No, a further firewall is not required
Yes, coat in fuel repellant stuff
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