G'day Mates

G'day mates. I have worked on various small woodworking projects in my spare time for many years. Right now I have a monster-sized project on my hands... rebuilding a bridge.

I need to figure out the most efficient way to cut two 3 cm deep by 35cm wide slots across 25 or so ~22cm wide Timbers that are the bridge "planks". The slots will fit into the two metal I-beams that stretch between the shorelines of the bridge.

I looked into Mortise and Dado blades, but the maximum width I could find was only about 3cm across and the feed rate was pretty slow.

I was thinking it would be more efficient to remove the majority of the whole 3cm x 35cm x 22cm block of wood at one time instead of trying to "chip" away at it. The only saw I could think of maneuvering and fitting sideways across the 120+kg Timbers to cut the bottom of the slot is a chainsaw! I was thinking of using a skillsaw to cut 3cm deep for the slot sides, then make some more cuts 3cm deep inside that than use the skillsaw at about a 45 degree angle to start cutting sections out so I can start to cut away enough room to use the chainsaw to clear away enough room so I can start to run the chainsaw sideways at 3cm in depth.

The slot does not have to be perfectly flat, just fairly flat so the timbers will lie at the same height when placed on the I-beams.

Is this a good way to do this? Any other ideas or tools I could use to get the job done efficiently?

I plan to post this same question in the "Big Stuff" forum, but figured I might as well post here so everyone who says G'day can see what I'm working on.

SupafastR