The Tamiya ones fit straight in but a tad pricey,the others need the lugs trimming off i think.
I have 2 types of lipo`s fitted in my TTG`s,the smaller one came from Dinball[RC Mart] and is listed to fit TTG`S the other ones came from Ebay,username revolutionshop i think,i had to get the measuring stick out,it was a bit tight and i had to cut a small hole in the side of the chassis to get room for the wiring to exit.
A standard RX will fit,brushless motors and speedo`s are well cheap for this scale IMO,be brave
PS, you can use Lipo`s with brushed motors and ESC`s[without safety cut off],just don`t run them totally flat or they die,as soon as you feel it slowing down bring it in and stop,let it cool off a bit and get some charge back in,they will be fine.