Tony,
I have done a little reserch on this.I am planning on putting a 1978 250 out of a nova along with the rear end from the nova and hookem together with a T-5 tranny B T W it is a 53 3100.
I have herd you can use the V-8 crossmember avalible at most venders for the side mount sixes,but Langdons Stovebolt sells a moter mount kit just for this conversion-this is what I plan on using -it looks like a neat clean setup.If you plan on useing O.E.gages the capilary tube for the temp gage is to short-Jim Carter sells one with a longer tube intended for V-8s but should work on 250 as well.You will also need a mount for the tranny-vendors sell a generic crossemember mount or you could fabricate.good luck. Aaron