Advise needed. building a tank "very little" to go on.

Hi all.

I am about to embark on a project of an SU-85T PZM.

It will be based on the upper hull of the Tamiya 1/35 SU-85 kit and I hope to put a dragon lower hull on it (but haven't gotton that far yet).

Their is very little information on this thing but it look's pretty cool.

I am only able to dig up 2 pic's and a side drawing of it and the experts that I have spoken with are only able to come up with the same.

My thought is that I can build this thing.

I want to know how the veteren scratch builders would go about doing a project like this?

I am thinking about taking mesurments off of the pics and scaling them down and drawing my own print to work from.

Will this work?

I want to make it as acurate as possable but I fear I may have to improvise in some areas.

(From what I know I will be able to get it pretty close)

Is it Kosher to do it this way?

Finaly, do you have any tips or hints?

Perhaps methods you use to build?

Thank you.