I have a 68 Fastback with an inline 6 300 and a manual. the car I believe had a 351 Windsor originally but a previous owner replaced it with the 300. ive decided to build the I6 because ive had a truck with one before and really love straight 6s anyway. This car is bone stock other than that and I was wondering if I could get some advice on how to get more power and maybe gas mileage out of it and what parts/companies to use. Im on a budget a little but ive got a few grand to put into it. I got a Exhaust manifold off of a 71 dumptruck that i read elsewhere were the best for these particular engines if you plan to turbo them down the road. The head needs redone so wanted to send it off the get rebuilt and possibly get it ported, port matched and polished but wanted to see if there are any alternative heads/ upgrades i should do first. Thanks in advance for any help.