I have a couple of questions. I have a tr4a that I started to restore frame off just been blasted. I now own a rustry tr6 with a very smooth engine. Should I use the 6 engine in the 4? would it drop right in? they made a tr 250 right? Would I see much perfomance improvenemts? O should I just go back with the origional 4 banger? thanks. Tony