Yep, I'm agreeing with Terry, again. It's starting to bother me, too, just doesn't seem right somehow...

An experienced head man absolutely would not do all that work unless they have hardened seats. Other than optimum cylinder compression sealing the heads are the single most important aspect of making power. Like Wally said, the 273 pieces may not even fit the 360 components, because '64-'65 273 heads have the bolt holes for intake manifold drilled at a different angle than all other LA engine heads.

First question: what's the head casting number?? Gotta know that to see what the guy started with, and what potential is even in the heads for use on a 360. '64-'65 273 heads were casting number 2465315, '66 273 were 2536178, '67 273-318 were 2658920, '68-'69 273-318 were 2843675.

Overall there's 2 types of heads used on LA's: the small port 273-318, and the LARGE port 360's. Only 3 stock valve combinations were used in stock configurations: 273-318 had 1.78 intake & 1.50 exhaust; '68-'71 340's had 2.02 intake & 1.60 exhaust. Stock 360, '72-'73 340, and 318 High Performance used 1.88 intake & 1.60 exhaust.

I used swirl port heads [with 3 angle valve job & beryllium-copper seats added] number 3418915 on my 360. Those were used on '71 360 and '72 340-360. Other 360 castings are 3671587 used in '73-'74, 3769974 used in '75 ['76 360 might have either of these head castings of #587 or #974], 4027596 & 4071051 used in '77-'79-'80.

Unless you $tumble upon $ome 2531894 340 heads, a good inexpensive option is the 360 head reworked to 340 specs. In addition there were 308's and several Mopar Performance heads, primarily for race use, not listing those here.

Very few people have the skills, experience and tools to do a truly high performance porting job. Mopar sells templates for porting, but that's only a small part of the process. You have to know how to use them, as a very basic guide, and have some way to chart progress, as in flow bench.

A guy wanting to [hopefully] teach himself head porting is likely to start by using a low budget set of heads to practice on, like maybe some 273 heads? An amateur home porting job often results in a set of heads that flow worse than stock!

Takes maybe a dozen sets of heads to start to get the hang of it. All intake ports & all exhaust ports must be identical to the others, not just eyeball similar. The only way to measure success or failure is the flow bench.

It's REAL easy to go too far, breaking into a water jacket, or be almost there, only find out too late when the head cracks. A DIY set of heads even if done well is only good for 5-15 horsepower.

A $25 - $100 set of stock 360 heads with a decent 3 angle valve job will flow the numbers off of a home-ported set of 273 heads and will have hardened seats, 'swirl' port design and much larger valves! If you want compression, shave them a bit.

Whatever you end up using, MAKE SURE YOU HAVE AT LEAST .055" clearance between piston crown and head, better to allow .080" total, minimum.