hi there i was in the same situation as you got the standard model chassis then later in the project decided to drop a 300 in it, they werent available to buy then but found some pictures and measurements and made my own worked fine. if you have some steel and are handy with a welder you could save yourself some pennies
I have used one top guy only lives up road bolted straight on and dropped straight in was just the turbo side was bit of a pain to do well get pics if you like tomorrow