looking to fix up an olds 403 for my truck

I have two 403's at the moment one in my truck and one i just tore down to rebuild for my truck. My rod is a 78 monte carlo which i have a 350/350 combo in it at the moment (i go through about an engine a year in that car). The other engine i had considered useing was a 403. The only reason that i did not use the 403 was that i wanted to keep the chev all chev. I will most likely be putting in a 427 with a 700 R4 next. But to the point i get great gas millage with a stock 403 in my 83 chev 3/4 ton which has 373 gears and a T400 tranny. I want to modify the replacment engine it's already bored 20 over with good rod bolts. I want to put a steel crank from a 330 in it and 72 350 heads as well as a mid range cam (it is a work truck) with an aluminum intake holly 780 vacume secondary. However i will retain manifolds as headers rot out fairly fast in this area (Northern Canada) But i have duel two inch exhaust. If you have any advice or suggestions that would be great.Any comments will be of interest to me thanks. And by the way the truck was not a diesel it was a standared with a 350 in it which was swapped for 403 for the improved fuel millage by the last owner who was partial to the 403 old's.

There are some great web sites on the Olds 350 diesel and how to build them with 403 parts.....