will 360 j heads fit on my 273

Another thing to note is that unless the J heads have been milled quite a bit and have aftermarket valves the chambers are close to 70 cc's.

A 302 head from a 88-91 318 roller engine might be a good improvement for the 273. I believe they are closed chambers and in the low 60's for cc's. Too bad your not close. A buddy of mine has a set of 302's for sale for a good price.

As far as the intake goes. It depends on what your doing with it. The performer is an ok choice but I believe the rpm is better. Definitely stick with a dual plane on a motor that small. Only problem is if you still have 273 heads the intake bolt pattern is different. The 273 head was an oddball because it was the only small block with a different intake bolt angle so a standard aftermarket intake that works on a 318-360 won't bolt up.