Meh we need a means of countering enemy armor on a large scale this year, not 5 years from now when we manage to build enough tanks.
Again: Why?
You are assuming two things: That we need a way to counter enemy armour this year, and that RPGs are the way to do that.
First: We need something to counter them this year. We don't, really. If we cannot strike them from Crow's Island with the resources we currently have, we have lost the island. If we can, we can choose the time for an invasion ourselves. In both cases, no need for this year.
Second: Producing RPGs may be a short-term solution, but will it actually be better than producing tanks? Well, if we assume the army to be completely armed with RPGs in two years (a very optimistic assessment), that makes sixty or more tanks we could've otherwise built without expanding the truck factory. Seeing as we've lost Mules vs their light tanks in a ratio of ca. 2:1 (more like 3:1 with the other support we've been given), we can assume that the produced tank will be able to reach more than parity. We do not know the actual number of enemy tanks, but they had three years of production time and got 57 knocked out, so they probably have less than a fifty remaining; about one hundred and fifty after two years. While this keeps us at a disadvantage, our design probably is better armed and armoured - at least, I'm assuming that for now.
Also, if you want quick anti-tank armament, why not simply use the 30mm cannon as an anti-tank gun? We could produce nearly two hundred and fifty of them if we take the capacity away from the 80mm and 160mm cannons currently not needed for other construction.
@Taricus: How about keeping the steam engine and implementing the other changes? That's something I would probably be agreeing about.