First off, the initial cost of an aftermarket n/A build is more than a power adder. If you sit down and add up parts/hp.
I did not realize that you had the 351 already. You might work on just getting the
suspension right the way you like it.
I would sell off those Ps and the gt40s on ebay and get some good parts for your 351. Shop around for some trick flow heads and grab a systemax II with a healthy cam before the motor ever goes in and just get your
suspension right first as you build.
The only Caveat is that a 351 swap even with your 400 dollar find is going to be a lot of money for very little HP and decent torque (good for a cruiser convertible pig). You need to add up the total cost of the swap and compare that to what it would cost just to slap an s-trim and gt40Ps and call it a day.
AFR 185s or TFS heads/ XE280/ systemax, shoud put you around 400/400 (give or take 15 hp) with all the neccessary boltons (351 headers/ full exhaust, Tb, injectors, pullies, MAF, fuel pump, FPR, tuning) A NEW HOOD! IT WILL NOT FIT UNDER A STOCK HOOD WITHOUT SERIOUS MODIFICATION AND PERFORMANCE SACRIFICING INTAKE. I'm sorry, I dont know if you saw this earlier.
S trim at 12 PSI / gt40 or performer will get you up around 400 in that neighborhood as well but wont have the same torque curve. (you will also need headers/full exhaust, MAF, Injectors fuel pump and tune.
These two cars will have extremely different street manners. One will be a booming cammed 351 and the other will be a sedate whining blower car with stockish manners until you take it into boost. There is nothing budget about a 351 swap especially one that needs a rebuild.
Tell us what your goals are and how much you can really spend over the next 2 years on the HP side, we will tell you what it will take to get there and give you several combos that will work. 2000, 3500, 5000, or 8000?